Error analysis of collimated and uncollimated SeHCAT retention measurement using a gamma camera

AIM

There is increasing interest in using collimated gamma cameras for [75Se]tauroselcholic acid (SeHCAT) studies to image the distribution and to make use of the collimator pressure sensitive devices (PSD) for patient safety. However, the use of a collimator will substantially decrease the sensitivity of the gamma camera. The aim of this article is to enable departments to calculate the uncertainty of SeHCAT retention measurements so that the acquisition time can be optimised to perform a reliable SeHCAT study.

METHOD

We derive a mathematical equation from the first principles that can be used to calculate the uncertainty in SeHCAT retention measurements on the basis of Poisson counting statistics. The equation takes account of background subtraction, use of the geometric mean for anterior/posterior attenuation compensation and the day 7 to day 0 quotient calculation.

RESULTS

Uncertainties in SeHCAT retention measurement using an intrinsic (uncollimated) gamma camera counting for 100 s are very low, typically of the order 15 ± 0.1%. Uncertainties from collimated gamma camera counting significantly increase for the same 100 s counting duration: 15 ± 0.8% for slim patients and 15 ± 4% for obese patients.

CONCLUSION

The acquisition time must be increased for collimated gamma camera SeHCAT counting to achieve acceptable counting statistics for an acceptable total uncertainty in the SeHCAT retention measurement. For slim patients, a minimum counting time of 2 min is required. For larger patients, the acquisition time needs to be increased to 30 min and further increased to 50 min for obese patients.

FXR Regulates Intestinal Cancer Stem Cell Proliferation

Increased levels of intestinal bile acids (BAs) are a risk factor for colorectal cancer (CRC). Here, we show that the convergence of dietary factors (high-fat diet) and dysregulated WNT signaling (APC mutation) alters BA profiles to drive malignant transformations in Lgr5-expressing (Lgr5+) cancer stem cells and promote an adenoma-to-adenocarcinoma progression. Mechanistically, we show that BAs that antagonize intestinal farnesoid X receptor (FXR) function, including tauro-β-muricholic acid (T-βMCA) and deoxycholic acid (DCA), induce proliferation and DNA damage in Lgr5+ cells. Conversely, selective activation of intestinal FXR can restrict abnormal Lgr5+ cell growth and curtail CRC progression. This unexpected role for FXR in coordinating intestinal self-renewal with BA levels implicates FXR as a potential therapeutic target for CRC.

A selective gut bacterial bile salt hydrolase alters host metabolism

The human gut microbiota impacts host metabolism and has been implicated in the pathophysiology of obesity and metabolic syndromes. However, defining the roles of specific microbial activities and metabolites on host phenotypes has proven challenging due to the complexity of the microbiome-host ecosystem. Here, we identify strains from the abundant gut bacterial phylum Bacteroidetes that display selective bile salt hydrolase (BSH) activity. Using isogenic strains of wild-type and BSH-deleted Bacteroides thetaiotaomicron, we selectively modulated the levels of the bile acid tauro-β-muricholic acid in monocolonized gnotobiotic mice. B. thetaiotaomicron BSH mutant-colonized mice displayed altered metabolism, including reduced weight gain and respiratory exchange ratios, as well as transcriptional changes in metabolic, circadian rhythm, and immune pathways in the gut and liver. Our results demonstrate that metabolites generated by a single microbial gene and enzymatic activity can profoundly alter host metabolism and gene expression at local and organism-level scales.

Update on Bile Acid Malabsorption: Finally Ready for Prime Time?

PURPOSE OF REVIEW

To provide an update on the prevalence, pathophysiology, disease associations, and treatment options for bile acid malabsorption (BAM).

RECENT FINDINGS

•Molecular mechanisms-BAs prevent water reabsorption and increase water secretion by intracellular mediators, increasing aquaporin channels and intracellular permeability. •Inflammatory bowel disease-new molecular mechanisms of BAM are identified in patients without ileal disease, including changes in expression of ileal BA transporter and nuclear receptors involved in BA homeostasis. •Microscopic colitis-BAM is one of the mechanisms leading to microscopic colitis. •Diagnostic testing-new diagnostic tests have been launched in the USA (serum C4 and fecal 48-h BA excretion); stimulated FGF19 has higher detection of BAM compared to fasting sample alone. •Treatment-investigational FXR agonists may provide a daily, oral option for treatment of BAM instead of BA sequestrants. There is a greater appreciation of the biological role of bile acids across multiple fields of medicine, including gastrointestinal indications.

The efficacy of a low-fat diet to manage the symptoms of bile acid malabsorption - outcomes in patients previously treated for cancer

Dietary fat ingestion triggers bile secretion into the gastrointestinal tract. Bile acid malabsorption affects >1% of the population, causing loose stool and other gastrointestinal symptoms. The diagnosis is frequently missed. Treatments are often considered ineffective. We evaluated low-fat diets for managing gastrointestinal symptoms in these patients. All patients reporting type 6 or 7 stool were offered a selenium-75 homocholic acid taurine (SeHCAT) scan. Prospective data in patients with 7-day scan retention <20% were analysed. -Patients requiring a bile acid sequestrant were given this before receiving dietary advice. Patients completed a 7-day food diary before dietetic consultations. Personalised dietary interventions, providing 20% of daily energy from fat, were prescribed. Symptoms were assessed using a modified gastrointestinal symptom rating scale questionnaire before and 4-12 weeks after dietary intervention. A total of 114 patients (49 male, median age 64 years, median body mass index 27 kg/m2) were evaluated. 44% of these patients were taking colesevelam. After dietary intervention, there was statistically significant improvement in abdominal pain and nocturnal defecation (0.2% alpha, p=0.001). Improvement in bowel frequency, urgency, flatulence, belching, borborygmi and stool consistency were seen, but did not reach statistical significance (p≤0.004-0.031). Dietary intervention is an effective treatment option for patients with symptomatic bile acid malabsorption and should be routinely considered.

Identification of a mouse Lactobacillus johnsonii strain with deconjugase activity against the FXR antagonist T-β-MCA

Bile salt hydrolase (BSH) activity against the bile acid tauro-beta-muricholic acid (T-β-MCA) was recently reported to mediate host bile acid, glucose, and lipid homeostasis via the farnesoid X receptor (FXR) signaling pathway. An earlier study correlated decreased Lactobacillus abundance in the cecum with increased concentrations of intestinal T-β-MCA, an FXR antagonist. While several studies have characterized BSHs in lactobacilli, deconjugation of T-β-MCA remains poorly characterized among members of this genus, and therefore it was unclear what strain(s) were responsible for this activity. Here, a strain of L. johnsonii with robust BSH activity against T-β-MCA in vitro was isolated from the cecum of a C57BL/6J mouse. A screening assay performed on a collection of 14 Lactobacillus strains from nine different species identified BSH substrate specificity for T-β-MCA only in two of three L. johnsonii strains. Genomic analysis of the two strains with this BSH activity revealed the presence of three bsh genes that are homologous to bsh genes in the previously sequenced human-associated strain L. johnsonii NCC533. Heterologous expression of several bsh genes in E. coli followed by enzymatic assays revealed broad differences in substrate specificity even among closely related bsh homologs, and suggests that the phylogeny of these enzymes does not closely correlate with substrate specificity. Predictive modeling allowed us to propose a potential mechanism driving differences in BSH activity for T-β-MCA in these homologs. Our data suggests that L. johnsonii regulates T-β-MCA levels in the mouse intestinal environment, and that this species may play a central role in FXR signaling in the mouse.

An Intestinal Farnesoid X Receptor-Ceramide Signaling Axis Modulates Hepatic Gluconeogenesis in Mice

Increasing evidence supports the view that intestinal farnesoid X receptor (FXR) is involved in glucose tolerance and that FXR signaling can be profoundly impacted by the gut microbiota. Selective manipulation of the gut microbiota-FXR signaling axis was reported to significantly impact glucose intolerance, but the precise molecular mechanism remains largely unknown. Here, caffeic acid phenethyl ester (CAPE), an over-the-counter dietary supplement and an inhibitor of bacterial bile salt hydrolase, increased levels of intestinal tauro-β-muricholic acid, which selectively suppresses intestinal FXR signaling. Intestinal FXR inhibition decreased ceramide levels by suppressing expression of genes involved in ceramide synthesis specifically in the intestinal ileum epithelial cells. The lower serum ceramides mediated decreased hepatic mitochondrial acetyl-CoA levels and pyruvate carboxylase (PC) activities and attenuated hepatic gluconeogenesis, independent of body weight change and hepatic insulin signaling in vivo; this was reversed by treatment of mice with ceramides or the FXR agonist GW4064. Ceramides substantially attenuated mitochondrial citrate synthase activities primarily through the induction of endoplasmic reticulum stress, which triggers increased hepatic mitochondrial acetyl-CoA levels and PC activities. These results reveal a mechanism by which the dietary supplement CAPE and intestinal FXR regulates hepatic gluconeogenesis and suggest that inhibiting intestinal FXR is a strategy for treating hyperglycemia.

Management of bile acid malabsorption using low-fat dietary interventions: a useful strategy applicable to some patients with diarrhoea-predominant irritable bowel syndrome?

This study evaluates the efficacy of low-fat dietary interventions in the management of gastrointestinal (GI) symptoms due to bile acid malabsorption. In total, 40 patients with GI symptoms and a 7-day (75)selenium homocholic acid taurine (SeHCAT) scan result of <20%, were prospectively recruited and then advised regarding a low-fat dietary intervention. Before and after dietary intervention, patients rated their GI symptoms using a 10-point numerical scale, and recorded their intake in 7-day dietary diaries. After dietary intervention, the median scores for all GI symptoms decreased, with a significant reduction for urgency, bloating, lack of control, bowel frequency (p ≥: 0.01). Mean dietary fat intake reduced to 42 g fat after intervention (p ≥: 0.01). Low-fat dietary interventions in patients with a SeHCAT scan result of <20% leads to clinically important improvement in GI symptoms and should be widely used.

Quantifying bile acid malabsorption helps predict response and tailor sequestrant therapy

Although recognised as a cause of chronic diarrhoea for over forty years, diagnostic tests and treatments for bile acid malabsorption (BAM) remain controversial. Recent National Institute for Health and Care Excellence (NICE) guidelines highlighted the lack of evidence in the field, and called for further research. This retrospective study explores the BAM subtype and severity, the use and response to bile acid sequestrants (BAS) and the prevalence of abnormal colonic histology. 264 selenium-75-labelled homocholic acid conjugated taurine (SeHCAT)-tested patient records were reviewed and the severity and subtype of BAM, presence of colonic histopathology and response to BAS were recorded. 53% of patients tested had BAM, with type-2 BAM in 45% of patients with presumed irritable bowel syndrome. Colonic histological abnormalities were similar overall between patients with (29%) or without (23%) BAM (p = 0.46) and between BAM subtypes, with no significant presence of inflammatory changes. 63% of patients with BAM had a successful BAS response which showed a trend to decreased response with reduced severity. Colestyramine was unsuccessful in 44% (38/87) and 45% of these (17/38) were related to medication intolerance, despite a positive SeHCAT. 47% (7/15) of colestyramine failures had a successful colesevelam response. No patient reported colesevelam intolerance. Quantifying severity of BAM appears to be useful in predicting BAS response. Colesevelam was better tolerated than colestyramine and showed some efficacy in colestyramine failures. Colestyramine failure should not be used to exclude BAM. Colonic histology is of no relevance.

The mechanism of increased biliary lipid secretion in mice with genetic inactivation of bile salt export pump

Human bile salt export pump (BSEP) mutations underlie progressive familial intrahepatic cholestasis type 2 (PFIC2). In the PFIC2 animal model, Bsep(-/-) mice, biliary secretion of bile salts (BS) is decreased, but that of phospholipids (PL) and cholesterol (CH) is increased. Under physiological conditions, the biliary secretion of PL and CH is positively related ("coupled") to that of BS. We aimed to elucidate the mechanism of increased biliary lipid secretion in Bsep(-/-) mice. The secretion of the BS tauro-β-muricholic acid (TβMCA) is relatively preserved in Bsep(-/-) mice. We infused Bsep(-/-) and Bsep(+/+) (control) mice with TβMCA in stepwise increasing dosages (150-600 nmol/min) and determined biliary bile flow, BS, PL, and CH secretion. mRNA and protein expression of relevant canalicular transporters was analyzed in livers from noninfused Bsep(-/-) and control mice. TβMCA infusion increased BS secretion in both Bsep(-/-) and control mice. The secreted PL or CH amount per BS, i.e., the "coupling," was continuously two- to threefold higher in Bsep(-/-) mice (P < 0.05). Hepatic mRNA expression of canalicular lipid transporters Mdr2, Abcg5, and Abcg8 was 45-55% higher in Bsep(-/-) mice (Abcg5; P < 0.05), as was canalicular Mdr2 and Abcg5 protein expression. Potential other explanations for the increased coupling of the biliary secretion of PL and CH to that of BS in Bsep(-/-) mice could be excluded. We conclude that the mechanism of increased biliary lipid secretion in Bsep(-/-) mice is based on increased expression of the responsible canalicular transporter proteins.

Bile acid signaling in lipid metabolism: metabolomic and lipidomic analysis of lipid and bile acid markers linked to anti-obesity and anti-diabetes in mice

Bile acid synthesis is the major pathway for catabolism of cholesterol. Cholesterol 7α-hydroxylase (CYP7A1) is the rate-limiting enzyme in the bile acid biosynthetic pathway in the liver and plays an important role in regulating lipid, glucose and energy metabolism. Transgenic mice overexpressing CYP7A1 (CYP7A1-tg mice) were resistant to high-fat diet (HFD)-induced obesity, fatty liver, and diabetes. However the mechanism of resistance to HFD-induced obesity of CYP7A1-tg mice has not been determined. In this study, metabolomic and lipidomic profiles of CYP7A1-tg mice were analyzed to explore the metabolic alterations in CYP7A1-tg mice that govern the protection against obesity and insulin resistance by using ultra-performance liquid chromatography-coupled with electrospray ionization quadrupole time-of-flight mass spectrometry combined with multivariate analyses. Lipidomics analysis identified seven lipid markers including lysophosphatidylcholines, phosphatidylcholines, sphingomyelins and ceramides that were significantly decreased in serum of HFD-fed CYP7A1-tg mice. Metabolomics analysis identified 13 metabolites in bile acid synthesis including taurochenodeoxycholic acid, taurodeoxycholic acid, tauroursodeoxycholic acid, taurocholic acid, and tauro-β-muricholic acid (T-β-MCA) that differed between CYP7A1-tg and wild-type mice. Notably, T-β-MCA, an antagonist of the farnesoid X receptor (FXR) was significantly increased in intestine of CYP7A1-tg mice. This study suggests that reducing 12α-hydroxylated bile acids and increasing intestinal T-β-MCA may reduce high fat diet-induced increase of phospholipids, sphingomyelins and ceramides, and ameliorate diabetes and obesity. This article is part of a Special Issue entitled Linking transcription to physiology in lipodomics.

Fate of ingested Clostridium difficile spores in mice

Clostridium difficile infection (CDI) is a leading cause of antibiotic-associated diarrhea, a major nosocomial complication. The infective form of C. difficile is the spore, a dormant and resistant structure that forms under stress. Although spore germination is the first committed step in CDI onset, the temporal and spatial distribution of ingested C. difficile spores is not clearly understood. We recently reported that CamSA, a synthetic bile salt analog, inhibits C. difficile spore germination in vitro and in vivo. In this study, we took advantage of the anti-germination activity of bile salts to determine the fate of ingested C. difficile spores. We tested four different bile salts for efficacy in preventing CDI. Since CamSA was the only anti-germinant tested able to prevent signs of CDI, we characterized CamSa’s in vitro stability, distribution, and cytotoxicity. We report that CamSA is stable to simulated gastrointestinal (GI) environments, but will be degraded by members of the natural microbiota found in a healthy gut. Our data suggest that CamSA will not be systemically available, but instead will be localized to the GI tract. Since in vitro pharmacological parameters were acceptable, CamSA was used to probe the mouse model of CDI. By varying the timing of CamSA dosage, we estimated that C. difficile spores germinated and established infection less than 10 hours after ingestion. We also showed that ingested C. difficile spores rapidly transited through the GI tract and accumulated in the colon and cecum of CamSA-treated mice. From there, C. difficile spores were slowly shed over a 96-hour period. To our knowledge, this is the first report of using molecular probes to obtain disease progression information for C. difficile infection.

An apoptosis-homing peptide-conjugated low molecular weight heparin-taurocholate conjugate with antitumor properties

Various angiogenesis inhibitors and apoptosis-targeting agents have been therapeutically applied in preclinical cancer models, some of which have been tested in clinical trials. In a previous study, we demonstrated that LHT7, a low molecular weight heparin (LMWH)-taurocholate conjugate, has strong antiangiogenic and tumor-suppressive activity and diminished anticoagulant properties. In this study, we developed LHT7-ApoPep-1, an apoptosis-homing peptide-conjugated variant of LHT7. LHT7-ApoPep-1 exhibited antiangiogenic activity in endothelial cell tube-formation assays and apoptotic cell-targeting ability in tumor cell binding assays; it also showed little toxicity toward healthy cells. Administration of LHT7-ApoPep-1 in mouse xenograft models of breast carcinoma delayed tumor growth compared to LHT7-only, and histological evaluations revealed decreased vessel formation and increased apoptotic area in tumor tissues. Moreover, an examination of LHT7-ApoPep-1-Cy7.5 localization within the body using in vivo live imaging showed accumulation at the tumor site of tumor-bearing mice, with a more prolonged circulation time and enhanced intensity compared to LHT7-Cy7.5. Inspection of the tumor microenvironment revealed that Cy5.5-labeled LHT7-ApoPep-1 was located on and near CD31-positive vessels in tumor tissue. We conclude that LHT7-ApoPep-1 has antiangiogenic and apoptosis-targeting properties and exerts antitumor effects by suppressing tumor vessel growth and homing to apoptotic cells within the tumor.

Cyclic RGDyk-conjugated LMWH-taurocholate derivative as a targeting angiogenesis inhibitor

LMWH-taurocholate derivative (LHT7) has been reported as a novel angiogenesis inhibitor, due to its ability to bind to several kinds of growth factors, which play critical roles in tumor angiogenesis. In this study, we have highlighted the enhanced antiangiogenic activity of LHT7, by using cyclic RGDyk (cRGD), a targeting moiety that was chemically conjugated to LHT7 via amide bond. The SPR study revealed that cRGD-LHT7 bound to α(v)β(3) integrin as strongly as cRGD, and it bound to VEGF as strongly as LHT7. Importantly, in vitro anti-angiogenesis studies revealed that cRGD-LHT7 had a significant inhibition effect on HUVEC tubular formation. Finally, cRGD-LHT7 showed a greater inhibitory efficiency on the tumor growth in the U87MG xenograft model than the original LHT7, which was owed to its ability to target the tumor cells. All of these findings demonstrated that cRGD-LHT7 targeted α(v)β(3) integrin-positive cancer cells and endothelial cells, resulting in a greater anti-angiogenesis effect on the solid tumors.

Bile acid malabsorption investigated by selenium-75-homocholic acid taurine ((75)SeHCAT) scans: causes and treatment responses to cholestyramine in 298 patients with chronic watery diarrhoea

BACKGROUND

The liver produces and secretes bile acids into the small intestine. In the small intestine, most of the bile acids are absorbed in the distal ileum with portal vein transportation back to the liver and resecretion (enterohepatic recycling). Increased spillover of bile acids from the small intestine into the colon (bile acid malabsorption) may affect the secretion of colonic water and electrolytes and result in watery diarrhoea. The aim of this study was to investigate the frequency of bile acid malabsorption and treatment responses to cholestyramine with (75)SeHCAT scanning among patients suffering from chronic watery diarrhoea.

METHODS

This was a retrospective study that included all patients who received a (75)SeHCAT scan over a five-year period (2004-2009).

RESULTS

In total, 298 patients (198 females, 100 men) with a median age of 42 years (range 16-82 years) were investigated. Bile acid malabsorption ((75)SeHCAT retention<15% after seven days) was identified in 201 patients (68%, 95% confidence interval (CI): 62%-73%). Bile acid malabsorption due to ileal dysfunction (Type I) was found in 77 patients, idiopathic bile acid malabsorption (Type II) was found in 68 patients and 56 patients with other conditions had bile acid malabsorption (Type III). Of the 150 patients who were able to take cholestyramine continuously, 108 patients (71%, CI: 63%-78%) reported a positive effect on their bowel habits.

CONCLUSIONS

Bile acid malabsorption is a frequent problem in patients with chronic watery diarrhoea. Treatment with bile acid binders was effective regardless of type and severity.

Use of novel cationic bile salts in cholesterol crystallization and solubilization in vitro

Unnatural bile salts have been synthesized with a cationic group at the side chain of natural bile acids. These cationic bile salts aggregate in water and aqueous salt solutions in a manner similar to their natural counterparts. The critical micellar concentrations of the cationic bile salts were measured using a fluorescence method. Cationic bile salts aggregated at a concentration lower than natural deoxycholic acid. Since dihydroxy bile salt micelles are well known for cholesterol dissolution/removal, the dissolution in the cationic micelles has been evaluated. The cationic analogs dissolve approximately 70 mg/dL of cholesterol, which is comparable to taurochenodeoxycholate micelle under identical bile salt concentrations. Cholesterol dissolution in cationic bile salt micelle enhanced upon adding various amounts of PC. Cholesterol crystallization was studied in model bile at various cationic bile salt concentrations. The addition of 5, 15 and 30 mM of the cationic bile salts attenuated the crystallization process, without influencing the crystal observation time or decreasing the final amount of crystals formed. All these effects were comparable to those observed with cholic acid. These findings suggest that cationic bile salts have physico-chemical properties analogous to those of natural anionic bile salts, and thus may have therapeutic potential.

Inhibition of bile acid transport across Na+/taurocholate cotransporting polypeptide (SLC10A1) and bile salt export pump (ABCB 11)-coexpressing LLC-PK1 cells by cholestasis-inducing drugs

Vectorial transport of bile acids across hepatocytes is a major driving force for bile flow, and bile acid retention in the liver causes hepatotoxicity. The basolateral and apical transporters for bile acids are thought to be targets of drugs that induce cholestasis. Previously, we constructed polarized LLC-PK1 cells that express both a major bile acid uptake transporter human Na+/taurocholate cotransporting polypeptide (SLC10A1) (NTCP) and the bile acid efflux transporter human bile salt export pump (ABCB 11) (BSEP) and showed that monolayers of such cells can be used to characterize vectorial transcellular transport of bile acids. In the present study, we investigated whether cholestasis-inducing drugs could inhibit bile acid transport in such cells. Because fluorescent substrates allow the development of a high-throughput screening method, we examined the transport by NTCP and BSEP of fluorescent bile acids as well as taurocholate. The aminofluorescein-tagged bile acids, chenodeoxycholylglycylamidofluorescein and cholylglycylamidofluorescein, were substrates of both NTCP and BSEP, and their basal-to-apical transport rates across coexpressing cell monolayers were 4.3 to 4.5 times those of the vector control, although smaller than for taurocholate. The well known cholestatic drugs, rifampicin, rifamycin SV, glibenclamide, and cyclosporin A, reduced the basal-to-apical transport and the apical efflux clearance of taurocholate across NTCP- and BSEP-coexpressing cell monolayers. Further analysis indicated that the drugs inhibited both NTCP and BSEP. Our study suggests that such coexpressing cells can provide a useful system for the identification of inhibitors of these two transport systems, including potential drug candidates.

Nasal drug delivery of sumatriptan succinate

The purpose of this work was to increase the nasal absorption of sumatriptan succinate by using bile salts. A rat in situ nasal perfusion technique was used to examine the rate and extent of absorption of sumatriptan succinate. In vitro enzymatic drug degradation studies were carried out with rat nasal washings. Various experimental conditions such as nasal perfusion rate, pH of the perfusion medium and concentrations of absorption enhancers such as sodium deoxycholate, sodium caprate, sodium tauroglycocholate and EDTA were optimized. In vivo studies were carried out for the optimized formulation in rabbits and the pharmacokinetics parameters of nasal solution were compared with marketed nasal solutions. Nasal absorption of sumatriptan succinate was pH dependent. It was found maximum at pH 5.5 and decreased at higher pH values. In in vitro enzymatic degradation studies, no measurable degradation was observed during the first week. The extent of drug absorption was increased by absorption enhancers. Sodium deoxycholate appeared to be more effective for enhancing the nasal absorption of sumatriptan succinate than the other absorption enhancers. The order of increasing absorption of sumatriptan succinate caused by theenhancers was sodium deoxycholate > sodium caprate > sodium tauroglycocholate > EDTA.

Intestinal absorption of the bile acid analogue 75Se-homocholic acid-taurine is increased in primary biliary cirrhosis, and reverts to normal during ursodeoxycholic acid administration

BACKGROUND

Whether ileal absorption of bile acid is up or downregulated in chronic cholestasis is still debated, and most evidence has come from animal studies.

AIMS

To compare ileal bile acid absorption in patients with primary biliary cirrhosis (PBC) and in healthy control subjects, and to assess the effect of ursodeoxycholic acid (UDCA).

PATIENTS

We studied 14 PBC patients before and during (n=11) UDCA administration, 14 healthy control subjects, and 14 Crohn's disease patients (as disease controls).

METHODS

We used cholescintigraphy to measure retention in the enterohepatic circulation over five successive days of the bile acid analogue (75)Se-homocholic acid-taurine ((75)SeHCAT) as an index of ileal bile acid absorption. Results were expressed as (75)SeHCAT fractional turnover rate (FTR) and t(1/2)12.

RESULTS

(75)SeHCAT FTR was 0.19 (0.11)/day, 0.34 (0.11)/day (p<0.001), and 0.83 (0.32)/day in PBC patients, healthy controls (p<0.0001), and Crohn's patients (p<0.001), respectively, which increased to 0.36 (0.16)/day in PBC patients during UDCA treatment (p<0.005). (75)SeHCAT t(1/2)12 was 4.8 (2.1) days in PBC patients, 2.2 (0.5) days (p<0.001) in healthy controls, and 1.0 (0.5) days (p<0.001) in Crohn's disease patients. (75)SeHCAT t(1/2)12 decreased to 2.2 (0.93) days (p< 0.001) in PBC patients during UDCA treatment.

CONCLUSIONS

Our results support the concept that ileal bile acid absorption is upregulated in PBC patients, and that this effect may contribute towards damaging the cholestatic liver. This upregulation of bile acid absorption is abolished by UDCA.

Bile acid malabsorption in patients with chronic diarrhoea: clinical value of SeHCAT test

BACKGROUND

Bile acid malabsorption (BAM), a cause of chronic diarrhoea, can be diagnosed by the SeHCAT test. The purpose of this study was to evaluate the usefulness of SeHCAT testing by assessing the extent of BAM and describing the clinical characteristics in a group of patients with chronic diarrhoea. Clinical outcome after treatment with cholestyramine was also evaluated.

METHODS

During a 5-year period (1997-2001) the SeHCAT test was performed in 135 patients in whom a primary programme for diagnostic evaluation of chronic diarrhoea had not revealed a cause. File data from 133 patients could be evaluated.

RESULTS

In 44% of patients, bile acid absorption was normal with SeHCAT retention > or = 15%. Impaired SeHCAT retention was found in 56%. All patients with ileocaecal resections had retention values < 10%. Patients with microscopic colitis presented with BAM in 39%. Only one patient with idiopathic BAM presented with steatorrhoea as opposed to 11 patients with type 1 and 3 BAM. Patients with idiopathic BAM and/or SeHCAT retention values < 5% had the best response to treatment with cholestyramine.

CONCLUSIONS

The SeHCAT test is of value in evaluation of patients with chronic diarrhoea as a second-line investigation with a high diagnostic yield. The only a priori parameter to predict BAM was the existence of ileocaecal resections. The result of the SeHCAT test seems to predict the benefit of treatment with cholestyramine.

Selective binding of steroids by 2,2'-biquinoline-4,4'-dicarboxamide-bridged bis(beta-cyclodextrin): fluorescence enhancement by guest inclusion

A novel bis(beta-cyclodextrin) was synthesized, and its binding behavior with steroids was investigated to demonstrate that the cooperative co-inclusion of guest and tether by two cyclodextrin moieties is operative to afford the highest molecular selectivity of up to 3.6 for deoxycholate over taurocholate.

Role of bile acids in lymphocytic colitis

BACKGROUND/AIMS

A high prevalence of bile acid malabsorption and a high response rate to bile acid binders are seen in collagenous colitis. Our aim was to explore if bile acids play a role in lymphocytic colitis, which is unknown.

METHODOLOGY

Patients with lymphocytic colitis completed a diagnostic program, including the 75SeHCAT (75Se-labelled homocholic acid-taurine) test and registration of symptoms. Prevalence of bile acid malabsorption, response to bile acid binders, correlation between 75SeHCAT and histopathology were determined. The 75SeHCAT values were compared with 29 controls.

RESULTS

Two out of 23 with lymphocytic colitis had a 75SeHCAT retention < or = 10%. The median 75SeHCAT value in lymphocytic colitis, 24% (range: 1.7-53), was lower than in the control group, 38% (range: 8-91) (P < 0.02). Forty-six per cent (6/13) responded to bile acid binders. No correlation was found between the 75SeHCAT values and degree of colonic inflammation. Two patients developed collagenous colitis.

CONCLUSIONS

Bile acid malabsorption is more uncommon in lymphocytic colitis than in collagenous colitis. The 75SeHCAT values, however, suggest a role of bile acids in lymphocytic colitis. The conversion of 2 patients to collagenous colitis and disturbed absorption of bile acids also in lymphocytic colitis is consistent with the idea that the two forms represent variants of the same disease.

Long-term course in collagenous colitis and the impact of bile acid malabsorption and bile acid sequestrants on histopathology and clinical features

BACKGROUND

Bile acid malabsorption is common in collagenous colitis, although long-term follow-up data on the impact of bile acids are limited. The aim was to study whether bile acid malabsorption is a permanent finding, with an impact on histopathology and clinical features in collagenous colitis.

METHODS

The objective was to reinvestigate 27 patients with collagenous colitis > or = 3 years after index investigation. The clinical course was evaluated by means of an interview, a review of the hospital records and registration of symptoms over a period of 7 days. The patients were invited to undergo a repeat colonoscopy and 75SeHCAT measurement. Initial and follow-up data and 75SeHCAT values from 29 controls were compared.

RESULTS

The median follow-up time was 4.2 (range 3-5.3) years. Twenty-two patients underwent a repeat 75SeHCAT test, 23 patients a colonoscopy and in 25 patients the clinical course could be evaluated. The 75SeHCAT values were abnormal in 32% at follow-up versus 44% at index, and the median retention value was 19% (range 2-69) versus 12% (range 0.5-41) (P = 0.024) although lower than in the control groups figure of 38% (range 8-91) (P < 0.005). Histopathology had improved independently of bile acid malabsorption, gender, smoking and autoimmune disease at follow-up. Four were normalized. Patients on bile acid binders had no significant change of histopathology. Four patients had recovered, seven displayed an intermittent course and 14 had continuous diarrhoea.

CONCLUSIONS

Collagenous colitis and bile acid malabsorption seem to be associated yet independent disorders. The histopathology improves during the long-term course although only a few patients resolve.

Design and properties of hepatitis C virus antisense oligonucleotides for liver specific drug targeting

Different backbone modified antisense oligonucleotides (AS-ODNs) directed against the hepatitis C virus genome were 5'-conjugated to cholesterol, cholic acid or taurocholic acid to enhance liver specific drug targeting and hepatocellular uptake. The lipophilic character of modified AS-ODNs was determined from RP-HPLC retention times and duplex stability was correlated with Tm-values from UV melting curves.

Bile acid malabsorption in persistent diarrhoea

We have investigated bile acid malabsorption (BAM), and its response to treatment, in patients seen in this district general hospital with chronic continuous or recurrent diarrhoea.

METHODS

Seven-day retention of 75-SeHCAT was measured (normal: > 10%).

TREATMENT

Patients were initially given conventional therapy (prednisolone +/- ASA drugs in Crohn's disease, and antidiarrhoeals in the others). If this therapy failed, bile acid sequestrants (BAS) were prescribed. The definition of successful response was based on the patient's perception of sustained improvement.

PATIENTS

The 304 patients were categorised as follows: Group 1: Crohn's disease patients with ileal resection, in clinical remission (n = 37). Group 2: Crohn's disease, unoperated and in clinical remission (n = 44). Group 3: vagotomy and pyloroplasty, with/without cholecystectomy (n = 26). Group 4: diarrhoea predominant 'irritable bowel syndrome' (IBS) (n = 197).

RESULTS

BAM was found in 97% (36/37), 54% (24/44) and 58% (15/26) of patients in groups 1, 2 and 3 respectively. One third (65/197) of patients with IBS had BAM. The outcome of treatment was available in 96 patients with BAM: of the patients with ileal resection 32% responded to antidiarrhoeals, 60% to BAS. Of the unoperated Crohn's patients 55% responded to disease-specific therapy, 40% to BAS. Of the gastric surgery patients 18% responded to conventional treatment, 64% to BAS. Of the IBS patients 15% of responded to conventional therapy, 70% to BAS.

CONCLUSIONS

This observational study indicates that BAM is common in patients with chronic diarrhoea, and is frequently found in IBS. The results of open treatment suggest that, where antidiarrhoeal drugs fail in such patients, BAS are often effective.

Intracellular supply of phospholipids for biliary secretion: evidence for a nonvesicular transport component

Phospholipids (PL) for biliary secretion could be supplied from the endoplasmic reticulum (ER) to the plasma membrane by cytosolic transfer proteins or transport vesicles. Therefore, we studied whether biliary secretions of PL and apolipoprotein A-I (apo A-I), as markers for the ER-to-Golgi vesicular transport pathway, are tightly coupled in isolated perfused rat livers with enhanced secretion (+60%) of PL after withdrawal of the cholesterol synthesis inhibitor pravastatin (0.1% of chow, fed for 7 days). Blocking agents dissociated the secretion of apo A-I and PL. Brefeldin A as well as cycloheximide inhibited biliary secretion of apo A-I (-52%; -68%), however, not of PL. Both bilirubin ditaurate and taurodehydrocholic acid reduced biliary secretion of PL (-27%; -79%), but not of apo A-I. The data support the concept that PL destined for biliary secretion bypass the vesicular transport pathway of apo A-I through the Golgi compartment, most likely via cytosolic transfer proteins.

Substrate specificity of the ileal and the hepatic Na(+)/bile acid cotransporters of the rabbit. II. A reliable 3D QSAR pharmacophore model for the ileal Na(+)/bile acid cotransporter

To design a reliable 3D QSAR model of the intestinal Na(+)/bile acid cotransporter, we have used a training set of 17 inhibitors of the rabbit ileal Na(+)/bile acid cotransporter. The IC(50) values of the training set of compounds covered a range of four orders of magnitude for inhibition of [(3)H]cholyltaurine uptake by CHO cells expressing the rabbit ileal Na(+)/bile acid cotransporter allowing the generation of a pharmacophore using the CATALYST algorithm. After thorough conformational analysis of each molecule, CATALYST generated a pharmacophore model characterized by five chemical features: one hydrogen bond donor, one hydrogen bond acceptor, and three hydrophobic features. The 3D pharmacophore was enantiospecific and correctly estimated the activities of the members of the training set. The predicted interactions of natural bile acids with the pharmacophore model of the ileal Na(+)/bile acid cotransporter explain exactly the experimentally found structure;-activity relationships for the interaction of bile acids with the ileal Na(+)/bile acid cotransporter (Kramer et al. 1999. J. Lipid. Res. 40: 1604;-1617). The natural bile acid analogues cholyltaurine, chenodeoxycholyltaurine, or deoxycholyltaurine were able to map four of the five features of the pharmacophore model: a) the five-membered ring D and the methyl group at position 18 map one hydrophobic site and the 21-methyl group of the side chain maps a second hydrophobic site; b) one of the alpha-oriented hydroxyl groups at position 7 or 12 fits the hydrogen bond donor feature; c) the negatively charged side chain acts as hydrogen bond acceptor; and d) the hydroxy group at position 3 does not specifically map any of the five binding features of the pharmacophore model. The 3-hydroxy group of natural bile acids is not essential for interactions with ileal or hepatic Na(+)/bile acid cotransporters. A modification of the 3-position of a natural bile acid molecule is therefore the preferred position for drug targeting strategies using bile acid transport pathways.

Prognosis of adult-onset idiopathic bile acid malabsorption

BACKGROUND

From 1986 to 1993, 150 patients were investigated with the 75Se-homocholic acid taurine (SeHCAT) test as a late step in the investigation of chronic diarrhoea. On basis of low SeHCAT values and response to cholestyramine treatment, 33 patients were initially classified as having idiopathic bile acid malabsorption (IBAM). The aim was to describe the long-term clinical course of the disease and to assess the reliability of the SeHCAT test in diagnosing IBAM.

METHODS

The methods included 1) clinical follow-up with patient interview combined with information from medical records and 2) repeated SeHCAT test.

RESULTS

The diagnosis of IBAM had to be revised in three cases (inflammatory bowel disease in two patients, Clostridium difficile infection in one). Six patients were lost to follow-up and a further four patients were excluded from re-examination either because of old age (>80 years) or bowel resection, leaving 20 patients for re-examination, of which 16 completed both clinical follow-up and a new SeHCAT test. The median duration of symptoms before initial SeHCAT test was 2.5 (1-30) years. In 13 of 16 patients symptoms persisted, and SeHCAT values remained low and almost identical to the initial value after a median observation time of 88 (51-113) months. Despite initial response to treatment with cholestyramine, six patients had to discontinue treatment because of adverse effects or other compliance problems. In three patients the SeHCAT value showed a considerable increase, and bowel function had correspondingly normalized in these cases.

CONCLUSION

The study confirms the reliability of the SeHCAT test in diagnosing IBAM. Despite adult onset of symptoms, only a few patients improve after several years' observation. Treatment with cholestyramine is generally effective but not always tolerated.

Transformation of bile acids and sterols by clostridia (fusiform bacteria) in Wistar rats

The effects on bile acid and sterol transformation of clostridia (fusiform bacteria), the dominant intestinal bacteria in rodents (ca. 10(10) counts per g wet feces) were examined in Wistar rats. After inoculation of clostridia into germ-free rats and into rats previously inoculated solely with Escherichia coli, most of the endogenous bile acids were deconjugated, and cholic acid and chenodeoxycholic acid were 7alpha-dehydroxylated to deoxycholic acid and lithocholic acid, respectively. Tauro-beta-muricholic acid, another major bile acid in rats, was deconjugated, but only part of it (ca. 30%) was transformed into hyodeoxycholic acid. Cholesterol and sitosterol were also reduced to coprostanol and sitostanol, respectively. Escherichia coli transformed neither bile acids nor sterols. These data suggest that clostridia play an important role in the formation of secondary bile acids and coprostanol in rats.

Bile acid malabsorption as a cause of chronic diarrhea: diagnostic value of 7alpha-hydroxy-4-cholesten-3-one in serum

To evaluate the usefulness of 7a-hydroxy-4-cholesten-3-one (HCO) serum concentrations as a diagnostic marker of bile acid malabsorption, we determined the reference range of HCO in 106 normal subjects (age 40.2+/-16.8 years; 55 women, 51 men) and conducted a utility study in 23 patients with chronic diarrhea of unknown origin (age 49.4+/-15.3 years, 13 women, 10 men). The diagnosis of bile acid malabsorption was made on the basis of a decreased retention of [75Se]homocholyltaurine after oral application (75SeHCAT test). HCO (reference range: 6-48 ng/ml) and the 75SeHCAT test yielded the same results in 19/23 (83%) patients. Bile acid malabsorption was identified by an increase of HCO in serum with a sensitivity of 90% and a specificity of 79%. Analysis of HCO in serum may serve as a novel, simple, and sensitive method for the detection of bile acid malabsorption in patients with chronic diarrhea of unknown origin.

Partial characterization of mechanisms of cytoprotective action of hydrophilic bile salts against hydrophobic bile salts in rats: relation to canalicular membrane fluidity and packing density

Bile salts regulate the subselection of phosphatidylcholine species secreted into bile and thereby modulate bile metastability. The aim of this study was to determine whether bile salts alter phosphatidylcholine species of the canalicular membrane, and if they do, to clarify whether the cytoprotective action of hydrophilic bile salts is associated with modulation of phosphatidylcholine composition in cell membrane bilayers. Bile salt-pool-depleted rats were infused intravenously with sodium taurocholate at a constant rate (200 nmol/min/100 g body wt) for 2 hr, followed by infusion of either sodium tauroursodeoxycholate, sodium tauroalphamuricholate, or sodium taurobetamuricholate (200 nmol/min/100 g) for 2 hr. Biliary outputs of cholesterol and phosphatidylcholine and phosphatidylcholine hydrophobicity in bile and subcellular fractions were determined. The cytoprotective action of hydrophilic bile salts was determined by the release of canalicular membrane-localizing enzymes (alkaline phosphatase, leucine aminopeptidase) into bile. Tauroursodeoxycholate, taurobetamuricholate, and tauroalphamuricholate decreased the release of these enzymes when compared to values under taurocholate infusion. Bile phosphatidylcholine hydrophobicity was also decreased by the bile salts, whereas the cholesterol/phosphatidylcholine ratio was increased. In contrast, phosphatidylcholine hydrophobicity in the canalicular membrane was increased by these three bile salts. In conclusion, hydrophilic bile salts promote biliary secretion of relatively hydrophilic phosphatidylcholine secretion into bile, and consequently phosphatidylcholine hydrophobicity in canalicular membranes increased. Such an alteration in phosphatidylcholine species within canalicular membrane enhances its lateral packing density with less fluidity, and this may account, in part, for the cytoprotective action of hydrophilic bile salts against hydrophobic bile salts.

Intestinal transport of gentamicin with a novel, glycosteroid drug transport agent

PURPOSE

The objective was to investigate the ability of a glycosteroid (TC002) to increase the oral bioavailability of gentamicin.

METHODS

Admixtures of gentamicin and TC002 were administered to the rat ileum by injection and to dogs by ileal or jejunal externalized ports, or PO. Bioavailability of gentamicin was determined by HPLC. 3H-TC002 was injected via externalized cannulas into rat ileum or jejunum, or PO and its distribution and elimination was determined. The metabolism of TC002 in rats was evaluated by solid phase extraction and HPLC analysis of plasma, urine and feces following oral or intestinal administration.

RESULTS

The bioavailability of gentamicin was substantially increased in the presence of TC002 in both rats and dogs. The level of absorption was dependent on the concentration of TC002 and site of administration. Greatest absorption occurred following ileal orjejunal administration. TC002 was significantly more efficacious than sodium taurocholate, but similar in cytotoxicity. TC002 remained primarily in the GI tract following oral or intestinal administration and cleared rapidly from the body. It was only partly metabolized in the GI tract, but was rapidly and completely converted to its metabolite in plasma and urine.

CONCLUSIONS

TC002 shows promise as a new drug transport agent for promoting intestinal absorption of polar molecules such as gentamicin.

Idiopathic bile acid malabsorption: qualitative and quantitative clinical features and response to cholestyramine

BACKGROUND

Idiopathic bile acid malabsorption is a poorly recognized cause of chronic diarrhoea. The SeHCAT (75Selenium HomotauroCholic Acid Test) can accurately diagnose this condition.

AIM

To identify patients with idiopathic bile acid malabsorption, to describe their clinical features, both qualitatively and quantitatively, and to assess the response to cholestyramine.

METHOD

Idiopathic bile acid malabsorption was considered in all patients complaining of chronic diarrhoea. They were included in the study if their SeHCATs were positive (< 15% retention) and secondary causes of bile acid malabsorption were excluded. The response to therapy with cholestyramine was assessed.

RESULTS

Nine patients were diagnosed with idiopathic bile acid malabsorption (median SeHCAT retention 8%, range 3-12.6). Their median daily faecal weight was 285 g (range 85-676) and median faecal fat output was 17 mmol/24 h (range 8.3-38.8). Six patients had an immediate response to cholestyramine. There was a marked reduction in stool frequency (median stool frequency pre-treatment 5/day vs. 2/day post-treatment, P = 0.03). Five patients had large volume diarrhoea (faecal weight > 200 g/day) and three had steatorrhoea.

CONCLUSIONS

Idiopathic bile acid malabsorption, once suspected, especially by documenting true 'large volume' watery diarrhoea or steatorrhoea, is easily diagnosed and response to therapy is often very good. There is often a previous history of gastrointestinal infection and this condition should be considered in patients with chronic diarrhoea of undetermined origin, especially before they are labelled as having irritable bowel syndrome.

Mechanisms of diarrhoea in myotonic dystrophy

BACKGROUND

Gastrointestinal (GI) symptoms are common in myotonic dystrophy (MD). Diarrhoea is one of the more disabling of these GI complaints. The mechanisms behind diarrhoea in MD have not previously been investigated systematically.

OBJECTIVE

To elucidate the mechanisms behind diarrhoea in MD.

METHODS

Twenty patients with MD and suffering from diarrhoea were investigated in order to detect malabsorption (blood tests and faecal fat excretion) and bile acid malabsorption ([75Se]selenahomocholic acid-taurine (SeHCAT) retention) and to study intestinal morphology (duodenal and rectal biopsies).

RESULTS

Two patients had deficiency of folic acid and four showed reduced levels of pancreatic isoamylase, but none of them had steatorrhoea. Two out of eight patients had abnormal bile acid breath tests with normal SeHCAT, indicating small bowel bacterial overgrowth and 12 displayed reduced SeHCAT retention. Duodenal biopsies were normal in eight patients and five out of nine rectal biopsies displayed slight inflammation.

CONCLUSIONS

A possible mechanism of diarrhoea in MD could be identified in most of the patients. Bile acid malabsorption seems to be a frequent cause and can be treated successfully.

Rapid hydrolysis of bile acid conjugates using microwaves: retention of absolute stereochemistry in the hydrolysis of (25R) 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestan-26-oyltaurine

In recent years, defects of bile acid synthesis caused by disorders of peroxisome biogenesis have led to increased interest in C27 bile acids. In humans, while the majority of bile acids are C24 carboxylic acids, the presence of increased concentrations of C27 bile acids and their metabolites in hereditary diseases associated with peroxisomal dysfunction can serve as a useful marker for the intensity of the metabolic disorder. Our present studies describe an efficient method for the rapid hydrolysis of C27 and C24 bile acid conjugates using a commercial microwave oven. The advantages of this method include freedom from racemization, minimal activation, mild reaction conditions, and the highly stereocontrolled nature of the reaction, thus allowing for free bile acid recovery in high yield. For example, when (25R) 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestan-26-oyl taurine, a major compound present in the bile of Alligator mississippiensis, was deconjugated with 4% NaOH/diethylene glycol or 1 M LiOH/propylene glycol in the microwave oven for 4-6 min, 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestan-26-oic acid (THCA) was obtained in 81% yield with retention of configuration at C-25. It is suggested that present studies will be helpful in delineating the absolute stereochemistry of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoyl-CoA oxidase, the peroxisomal enzyme that catalyzes the first step in the oxidation of THCA.

Chlorambucil-taurocholate is transported by bile acid carriers expressed in human hepatocellular carcinomas

BACKGROUND & AIMS

Chemotherapy of hepatocellular carcinomas is hampered by the insufficient accumulation of cytostatic drugs within the tumor cells. The aim of this study was to evaluate the feasibility of therapeutic strategies using antineoplastic agents coupled to bile acids.

METHODS

Expression of the Na(+)-taurocholate-cotransporting polypeptide (NTCP) was analyzed in six hepatocellular carcinomas and in nonmalignant liver tissue. Uptake of the cytostatic drug [3H]-chlorambucil-taurocholate (S2676) was measured in Xenopus laevis oocytes injected with total messenger RNA (mRNA) from the carcinomas or peritumor tissue or with complementary RNA encoding the NTCP or the organic anion-transporting polypeptide (OATP) of human liver.

RESULTS

Expression of hepatocellular carcinoma mRNA in oocytes resulted in mainly Na(+)-dependent uptake of chlorambucil-taurocholate. The level of NTCP mRNA in carcinomas amounted to 56% +/- 27% compared with peritumor tissue. Immunofluorescence studies confirmed the expression of NTCP on the surface of hepatocellular carcinoma cells. OATP expression, determined by immunoblotting, was similar in hepatocellular carcinomas and surrounding liver tissue (n = 3). NTCP mediated Na(+)-dependent uptake of chlorambucil-taurocholate (Michaelis constant, 11 mumol/L), whereas OATP mediated Na(+)-independent uptake.

CONCLUSIONS

Hepatocellular carcinomas express the Na(+)-dependent bile acid transporter NTCP. Because NTCP mediates high-affinity uptake of chlorambucil-taurocholate, targeting of cytostatic bile acids to hepatocellular carcinomas could become a feasible therapeutic strategy.

Role of bile salts in colchicine-induced hepatotoxicity. Implications for hepatocellular integrity and function

Colchicine, a microtubule-disrupting agent, induces hepatotoxicity in experimental animals at the doses commonly employed to explore vesicular transport in the liver. The effect of manipulations of the bile salt pool on colchicine-induced hepatotoxicity was studied in rats to determine the role of bile salts in this phenomenon. Leakage of enzyme markers of liver-cell damage into plasma and bile induced by colchicine pre-treatment displayed a sigmoidal log dose-effect curve, the half-maximal effect being reached at 0.12 micromol per 100 g body wt. Lumicolchicine, instead, showed no harmful effect. Maximal increment of biliary LDH discharge induced by colchicine was reduced from 950 +/- 124% to 216 +/- 29% by bile diversion leading to a marked reduction in bile salt output, and this parameter was further decreased to 100 +/- 13% and 157 +/- 39% by subsequent repletion of the bile salt pool with the hydrophilic bile salts taurodehydrocholate and tauroursodeoxycholate, respectively. Conversely, infusion of taurocholate into non-bile salt depleted, colchicine-treated rats led to cholestasis and massive discharge of enzymes into both blood and bile. Our data show conclusively that colchicine-induced hepatotoxicity depends on the magnitude and composition of the bile salt flux traversing the liver. They also support the view that functional integrity of vesicular mechanisms presumably involved in membrane repair are indispensable to protect the hepatocytes from the damaging effect of bile salts during normal bile formation.

Uptake of 3 alpha, 7 alpha, 12 alpha-trihydroxy-24-nor-5 beta-cholan-23-sulfonate into isolated rat hepatocytes by three transport systems

Uptake of norcholansulfonate (3 alpha, 7 alpha, 12 alpha-trihydroxy-24-nor-5 beta-cholan-23-sulfonate), an isogeometric analogue of cholate into isolated rat liver hepatocytes occurs only by saturable transport. In order to identify the transport systems involved, uptake of norcholansulfonate was studied using 7 beta-NBD-NCT ({N-[7-(4-nitrobenzo-2-oxa-1,3-diazol)]-7 beta-amino-3 alpha,12 alpha-dihydroxy-5 beta-cholan-24-oyl})-2'-aminoethanesulfonate) as a competing substrate. For transport of both bile salt derivatives, which mutually inhibit their mediated transport competitively, the existence of at least three transport systems must be assumed. Uptake studies using the cloned hepatic Na+/cholyltaurine cotransporting polypeptide stably expressed in CHO cells (Chinese hamster ovary cells) showed that both bile salt derivatives were transported and furnished the definite KT values of this single transport system and the ratio of the maximal uptake velocities. On the basis of these data, uptake of both bile salt derivatives into rat hepatocytes and their mutual competitive inhibition could be analyzed for three transport systems. The maximal flux rates J2 and the half-saturation constants KT2 in the presence of Na+ (143 mM) are for norcholansulfonate: J1(Na+ 143) = 1.0 +/- 0.2 nmol/(min . mg protein), KT1(Na+ 143) = 15 +/- 4 microM, J2(Na+ 143) = 0.5 +/- 0.2 nmol/(min.mg protein), KT2(Na+ 143) = 15 +/- 2 microM, J3(Na+ 143) = 0.5 +/- 0.2 nmol/(min.mg protein), KT3(Na+ 143) = 60 +/- 15 microM, and for 7 beta-NBD-NCT J1(Na+ 143) = 0.14 +/- 0.04 nmol/(min.mg protein), KT1(Na+ 143) = 3.1 +/- 0.5 microM, J2(Na+ 143) = 0.014 +/- 0.005 nmol/(min.mg protein), KT2(Na+ 143) = 21 +/- 2 microM, J3(Na+ 143) = 1.0 +/- 0.1 nmol/(min.mg protein), KT3(Na+ 143) = 190 +/- 25 microM. The kinetic parameters are in accordance with the assumptions that the cloned Na+/cholyltaurine cotransporting polypeptide represents transport system 2 and that the kinetically identified additional transport system 1 is either strictly or partially Na(+)-dependent.

Effect of tauro-alpha-muricholate and tauro-beta-muricholate on oestradiol-17 beta-glucuronide-induced cholestasis in rats

The effect of tauro-beta-muricholate (beta MC-tau) and tauro-alpha-muricholate (alpha MC-tau) on oestradiol-17 beta-glucuronide (E217G)-induced cholestasis was compared with that of tauroursodeoxycholate (UDC-tau) in rats. Like UDC-tau, alpha MC-tau and beta MC-tau infused at the rate of 0.2 mumol/min per 100 g bodyweight (BW) completely inhibited the cholestasis induced by E217G infused at the rate of 0.06 mumol/min per 100 g BW for 20 min. These findings indicate that beta MC-tau and alpha MC-tau are useful in protecting against various types of experimental cholestasis, as well as against bile acid-induced cholestasis.

Ileal absorption of bile acids in patients with chronic cholestasis: SeHCAT test results and effect of ursodeoxycholic acid (UDCA)

The effect of cholestasis on ileal bile acid absorption is controversial in animal models (up- or down-regulation) and unknown in humans. We therefore studied values of the selena homotaurocholic acid (SeHCAT) test before and after long-term administration (>3 months, 13-15 mg/kg/day) of ursodeoxycholic acid (UDCA) in 27 patients with chronic cholestatic liver diseases (24 women, 3 men; mean age, 50 years; 24 primary biliary cirrhosis, 2 secondary biliary cirrhosis, 2 others). The control group consisted of 14 healthy volunteers. Seven-day SeHCAT percentage retention was identical in the 12 untreated cholestatic patients (serum bilirubin, 75+/-42 micromol/L, alkaline phosphatase, 4.2+/-1.0 N; mean+/-SEM) and in the control group (43.6+/-2.9 and 43.8+/-4.2%, respectively). In the 22 patients treated by UDCA for 38+/-8 months, SeHCAT percentage retention was 20.3+/-3.0%. In the seven patients with the SeHCAT test done before and after UDCA treatment (16+/-5 months), SeHCAT percentage retention decreased significantly under UDCA therapy (42.0+/-4.4 vs 19.4+/-4.1%; P < 0.02). We conclude that, in patients with chronic cholestasis (1) SeHCAT percentage retention is not altered-taken together with the known defect of biliary excretion, this lack of increase in SeHCAT percentage retention argues against up-regulation of bile acid ileal transport; and (2) UDCA treatment induces a decrease in the SeHCAT percentage retention-this effect may be related primarily to a decreased bile acid ileal absorption.

Radiological bile acid absorption test 75SeHCAT in patients with diarrhoea of unknown cause

PURPOSE

The purpose with this study was to investigate the usefulness of the 75SeHCAT test in patients suffering from "functional" diarrhoea and to disclose earlier radiological investigations performed in the course of disease.

MATERIAL AND METHODS

Twenty patients with chronic diarrhoea of unknown cause were investigated with the 75SeHCAT test. The cholestyramine test and an estimation of oro-caecal transit time (OCTT) were also performed in 13 and 10 patients respectively.

RESULTS

Ten patients had low 7-day retention (< or = 15%). Nine of these were tested with cholestyramine and 8 showed complete relief from the diarrhoea. The cholestyramine test had no effect on the 4 patients with normal bile acid retention. No correlation was found between the retention of 75SeHCAT and OCCT. A total of 80 inconclusive gastrointestinal barium examinations were performed during the course of disease.

CONCLUSION

Pathological bile acid retention, studied with the radiological 75SeHCAT test, is common in patients with diarrhoea of unknown cause. The test should be performed earlier in the course of disease in order to prevent unnecessary radiological investigations and to reduce patient suffering and distress.

Bile acid malabsorption in HIV infected patients with chronic diarrhoea

AIMS

To look for the presence of bile acid malabsorption in HIV infected patients with chronic diarrhoea and determine whether bile sequestering agents may have a role in palliating this common problem.

METHODS

Nineteen HIV infected patients with chronic diarrhoea (duration > one month) poorly controlled on conventional treatment were investigated using the seven day retention of 75seleno-23-homocholic acid taurine (SeHCAT) as a measure of bile acid loss from the enterohepatic circulation. Patients with evidence of bile acid malabsorption were offered cholestyramine.

RESULTS

Sixteen (84%) had evidence of bile acid malabsorption (< 15% retention at seven days). Ten of the 16 patients with bile acid malabsorption had terminal ileal biopsies-six had ileitis and four normal histology, suggesting that malabsorption is not always related to terminal ileitis. Thirteen patients with bile acid malabsorption have been treated with cholestyramine and 11 have reported a symptomatic response.

CONCLUSIONS

Bile acid malabsorption can be demonstrated in some cases of HIV associated chronic diarrhoea and we suggest a therapeutic trial of a bile sequestering agent in patients whose symptoms are not well controlled using conventional anti-diarrhoeal agents.

Gastric antrectomy with selective gastric vagotomy does not influence gallbladder motility during interdigestive and postprandial periods

Fasting gastrointestinal motility and gallbladder motility during the interdigestive state and in the postprandial period was studied in eight patients who were operated for ulcer disease with an antrectomy and selective gastric vagotomy. Nocturnal motility recording revealed all three phases of the migrating motor complex (MMC) in all but one patient, where no phase III activity was recorded. In the rest of the patients 3-10 events with phase III activity were recorded. At scintigraphy ([75Se]HCAT) a cyclic gallbladder filling and emptying in relation to the MMC cycle was found. Episodes with emptying were confined to phase II and a total of 13 episodes with a median duration of 25 min (range 10-70 min) were observed. A median of 10.7% (6.1-17.7%) of the gallbladder contents was emptied. In a control group of eight healthy young men the values were 13.5 min (9-36 min) and 6.9% (3.7-31.1%), respectively. These differences were not significant. During the postprandial period, a lag period in gallbladder emptying of median 15 min (5-20 min) was observed when food ingestion took place during phase I of the MMC. Thereafter a gradual emptying occurred with a rate of 0.95% min (0.71-1.15%/min). In a control group of healthy young males, the lag period was 13.5 min (9-22.5 min) and the emptying rate 0.61%/min (0.08-0.77%/min). When food ingestion occurred during phase II of the MMC, the lag period of gallbladder emptying in the patient group was median 0 min (0-5 min) and the emptying rate was 0.77%/min (0.33-0.86%/min). The values in the control group were 0 min (-9 to 13.5 min) and 0.76%/min (0.54-2.25%/min), respectively. These differences between the patients and controls were not significant. In conclusion, antrectomy and selective gastric vagotomy do not influence fasting gastrointestinal motility or gallbladder motility during the interdigestive state or in the postprandial period.

Plasma lathosterol as a screening test for bile acid malabsorption due to ileal resection: correlation with 75SeHCAT test and faecal bile acid excretion

1. Plasma lathosterol concentration, known to reflect cholesterol and bile acid synthesis, was evaluated as a screening test for bile acid malabsorption, comparing it with faecal bile acid measurements, SeHCAT test and Schilling test in 22 subjects of whom six were healthy controls and 16 had Crohn's disease with ileal resections of varying length. 2. Plasma lathosterols and other non-cholesterol sterols were determined by GLC. Faecal bile acids were measured by GLC, and SeHCAT retention times by gamma camera. The study subjects were divided into two groups according to the degree of bile acid malabsorption: controls (faecal bile acids < 10 mg day-1 kg-1, n = 9) and bile acid malabsorption (faecal bile acids > 10 mg day-1 kg-1, n = 13). 3. Faecal bile acid excretion was 5.9 +/- 1.0 mg day-1 kg-1 in control subjects and 45.7 +/- 6.1 mg day-1 kg-1 in the bile acid malabsorption group. The biological half-life of 75SeHCAT (T1/2) was 95.6 +/- 16.3 h and 14.1 +/- 4.1 h, respectively. Plasma lathosterol levels were significantly elevated in patients with bile acid malabsorption (742 +/- 84 micrograms/ml compared with 400 +/- 59 micrograms/ml in control subjects) and correlated closely with faecal bile acid levels (r = 0.779, P < 0.001), with 75SeHCAT T1/2 (r = -0.524, P < 0.05) and with Schilling test (r = -0.591, P < 0.05). Significant correlations were also obtained for delta 8-cholestenol with faecal bile acids (r = 0.784, P < 0.001) and 75SeHCAT (r = -0.505, P < 0.05). The biological half-life of SeHCAT correlated with faecal bile acid excretion (r = -0.702, P < 0.001). Using mean+2 SD of lathosterol (In micrograms/ml cholesterol) as a cut-off value and 10 mg day-1 kg-1 as the upper limit for faecal bile acid excretion, the test gives 100% sensitivity and 82% specificity for plasma lathosterol determination to detect bile acid malabsorption. 4. The results indicate that both the 75SeHCAT test and plasma lathosterol detect bile acid malabsorption in patients with ileal resections for Crohn's disease. However, plasma lathosterol is a simpler and less expensive method.

Serum 7 alpha-hydroxy-4-cholesten-3-one and selenohomocholyltaurine (SeHCAT) whole body retention in the assessment of bile acid induced diarrhoea

OBJECTIVE

To assess the reliability of serum 7 alpha-hydroxy-4-cholesten-3-one (7 alpha-3ox-C) in the differential diagnosis of bile acid induced diarrhoea by comparison with 75selenohomocholyltaurine whole body retention (SeHCAT WBR).

DESIGN

One hundred and sixty-four patients with chronic diarrhoea were investigated prospectively in two centres (Edinburgh and Sweden) by two different tests which measure bile acid loss or synthesis: the SeHCAT test which measures the 7-day SeHCAT WBR and serum 7 alpha-3ox-C which reflects the rate of bile acid synthesis.

RESULTS

Forty-six patients had SeHCAT WBR of less than 10% (19 with ileal disease or resection, nine with idiopathic bile acid induced diarrhoea and 18 with miscellaneous causes for bile acid induced diarrhoea). All patients with ileal or idiopathic disease showed a favorable response to treatment as did 13 of the miscellaneous group. Serum 7 alpha-3ox-C was raised in all subjects with ileal disease/resection, seven patients with idiopathic disease and all subjects in the miscellaneous group who responded to treatment. Sixteen out of 118 patients with SeHCAT WBR greater than or equal to 10% had raised serum 7 alpha-3ox-C.

CONCLUSION

The positive predictive value of serum 7 alpha-3ox-C was 74%. The high negative predictive value (98%) of serum 7 alpha-3ox-C indicates the possible use of this test for excluding bile acid malabsorption in this population. All but two subjects who responded to treatment had raised serum 7 alpha-3ox-C concentrations. The possibility that the sensitivity of the test can be improved by repeat testing needs to be further investigated. There was a significant correlation between fractional catabolic rate (FCR) SeHCAT and serum 7 alpha-3ox-C (r = 0.63, P < 0.0001). Further data are required to validate the reference range in women over 70 years of age.

HIV-enteropathy and bile acid malabsorption: response to cholestyramine

Chronic diarrhea and weight loss are common in patients with AIDS. We report on an AIDS patient with chronic diarrhea, steatorrhea, and marked weight loss. A 75SeHCAT test demonstrated that the diarrhea was mainly due to bile acid malabsorption. Therapy with cholestyramine dramatically reduced bowel movements and led to significant reversal of weight loss.

Enhancement of Mdr2-mediated phosphatidylcholine translocation by the bile salt taurocholate. Implications for hepatic bile formation

Expression of the Mdr2-protein in secretory vesicules (SVs) from the yeast mutant sec6-4 causes a time- and temperature-dependent enhancement of phosphatidylcholine (PC) translocation from the outer to the inner leaflet of the SV lipid bilayer. We show that this activity is independent of changes either in the membrane potential or the pH gradient (inside positive) generated in these SVs by the yeast proton-translocating PMA1 ATPase. However, loading of the SVs with the primary bile salt taurocholate results in an apparent enhancement of Mdr2-mediated PC translocation activity. Reducing the intravesicular taurocholate (TC) concentration by dissipating the electrochemical potential across the SV membranes eliminates the enhancing effect of TC. Three lines of evidence suggest that the enhanced Mdr2-mediated PC translocation activity is not caused by a regulatory effect of TC on Mdr2 but rather reflected the formation of TC/PC aggregates or micelles in the lumen of SVs. First, significantly higher detergent concentrations are required to reveal the fluorescence of (7-nitro-2-1,3-benzoxadiazol-4-yl)amino-PC molecules translocated in Mdr2-SV under conditions of TC stimulation than under control conditions; second, the nonmicelle-forming bile salt taurodehydrocholate does not cause enhancement of PC translocation in Mdr2-SVs; third, enzyme marker studies indicate that TC behaves as a potent lipid solubilizer directly extracting PC molecules out of the bilayer without causing leakage. This results in the formation of intravesicular aggregates or mixed micelles, and provokes the apparent stimulation of Mdr2 activity. These data demonstrate a unique relationship between Mdr2, PC, and TC in the process of bile formation and secretion.

Direct assessment of the mechanism for a raised serum bile acid level in chronic liver disease

BACKGROUND

Impaired hepatic uptake is the major cause of raised serum bile acid levels in liver disease, but confirmation in humans by direct measurement is lacking. The synthetic gamma-labelled bile acid 75Se-homocholic acid taurine (75SeHCAT) provides a tool for the direct measurement of hepatic bile acid handling.

OBJECTIVE

To determine the interrelationships among hepatic handling of 75SeHCAT, the kinetics of its disappearance from plasma and serum bile acid levels in patients with chronic liver disease.

DESIGN

We studied 12 patients with primary biliary cirrhosis and 14 with cirrhosis arising from other causes. Fasting serum bile acid levels were measured enzymatically. After intravenous administration of 75SeHCAT, we determined plasma disappearance rates (initial K1, late K2) from serial blood samples and hepatic uptake and excretory rates directly from dynamic abdominal gamma-camera scanning. Both scanning and sampling were carried out over a period of 90 min.

RESULTS

Serum bile acid concentrations correlated with K1 and with hepatic uptake (Rs = -0.53, P < 0.01; Rs = -0.47, P < 0.02, respectively) but neither with K2 nor with the excretory rate. K1 and uptake were reduced (P < 0.05) in patients with high serum bile acid levels and in those with varices. Serum bile acid levels were higher in patients with varices (P < 0.05), which might suggest that portosystemic shunting occurred. However, this is unlikely because the varices were not independent of liver function.

CONCLUSION

Hepatic bile acid uptake and excretion are independent processes. Hepatic uptake is related to initial, whereas hepatic excretion is related to late, plasma disappearance. Impaired hepatic uptake is a major determinant of the rise in serum bile acid levels in chronic liver disease.