Hyperalphalipoproteinaemic activity of BRL 26314--I. Enhanced cholesterol turnover in rats

Administration of BRL 26314 [N-(4-chlorobenzyl)-L-phenylalanine] raises circulating high-density lipoprotein (HDL) cholesterol and lowers total triglyceride levels in rats whether maintained on stock or semi-synthetic diets. HDL is also elevated by BRL 26314 in hypothyroid rats and in rats with pre-existing hyperlipidaemia where aortic total cholesterol concentration is decreased. BRL 26314 promotes the excretion of a dose of radiolabelled cholesterol as faecal sterols and bile acids, and decreases the extent of cholesterol-radiolabelling in tissue pools, particularly the aorta and adipose tissue. The increase in cholesterol and bile acid (cholic acid) turnover distinguishes BRL 26314 from a cholestatic agent such as 1-naphthyl isothiocyanate where a superficially similar change in HDL concentration disguises an impaired cholesterol transport. BRL 26314 is not a general protein inducer but part of the mechanism of action may involve enhancement of white adipose tissue lipoprotein lipase activity.     

Absorption of taurocholic acid by the ileum of normal and transgenic DeltaF508 cystic fibrosis mice

Changes in intestinal transport in cystic fibrosis (CF) include both defective Cl(-) secretion and alterations in absorption. This study focused on the effects of CF on the active re-absorption of bile acids in the ileum of normal and transgenic CF mice. Taurocholic acid absorption was monitored as changes in short-circuit current (SCC) in intact and stripped ileal sheets from normal (Swiss) and transgenic CF (Cftr(tm2Cam)) mice with the DeltaF508 mutation. Taurocholic acid uptake was measured directly in everted ileal sacs and in brush-border membrane vesicles (BBMVs) using radiolabelled bile acid. Taurocholic acid caused a biphasic increase in SCC in both intact and stripped ileal sheets from Swiss mice. The initial phase of the response was associated with active bile acid absorption as it was inhibited by a low mucosal Na(+) concentration, but unaffected by Cl(-)-free conditions, serosal furosemide or mucosal diphenylamine-2-carboxylic acid (DPC). The first phase was concentration-dependent and was reduced in the presence of other actively transported bile acids. Intact ileal sheets from wild-type Cftr(tm2Cam) mice also exhibited a biphasic SCC response to taurocholic acid, but in CF tissues the initial phase was reduced and the second phase was absent. Taurocholic acid was actively taken up by everted ileal sacs from Swiss mice. This process was inhibited by a low mucosal Na(+) concentration or the presence of other actively transported bile acids. A similar taurocholic acid uptake was observed in ileal sacs from wild-type mice, but in those from CF mice transport of the bile acid was significantly reduced. However, taurocholic acid uptake was similar in BBMVs from wildtype and CF ilea. Active absorption of taurocholic acid occurs in mouse ileum and this process is reduced in transgenic mouse models of CF with the DeltaF508 mutation. However, this difference cannot be detected in an isolated preparation of brush-border membranes.     

Altered bile acid metabolism in alloxan diabetic rats

Changes of cholesterol, phospholipid, triglyceride or bile acid levels in serum liver, bile and feces after the treatment with alloxan were examined in Wistar strain male rats. Serum cholesterol, phospholipid and triglyceride levels and liver cholesterol level markedly increased but liver phospholipid and triglyceride levels remained unchanged. The lipid levels in serum very low density and low density lipoproteins were elevated but those in high density lipoprotein were not. Bile flow was not changed but biliary secretion of cholesterol, phospholipid and bile acids markedly increased. Among the biliary bile acid components, cholic acid markedly increased but the amount of chenodeoxycholic acid was similar to that of normal rats. Fecal excretion of deoxycholic acid increased but that of lithocholic and hyodeoxycholic acids decreased, and alpha, beta- and omega-muricholic acids did not change, thus, the total amount of fecal bile acids remained unchanged. Hepatic cholesterol synthesis was markedly depressed, while cholesterol 7 alpha-hydroxylase activity did not change and cytochrome P-450 content was elevated by about 40%. From such evidence, it was apparent that synthesis of cholic acid increased while that of chenodeoxycholic acid decreased and the total amount of bile acids synthesized did not change in the diabetic rats. Furthermore, marked increase of the pool size of cholic acid and hepatic secretion of cholic acid stimulated the absorption of lipids and produced a hyperlipidemia in the diabetic rats.     

Novel non-systemic inhibitor of ileal apical Na+-dependent bile acid transporter reduces serum cholesterol levels in hamsters and monkeys

1-{7-[(1-(3,5-Diethoxyphenyl)-3-{[(3,5-difluorophenyl)(ethyl)amino]carbonyl}-4-oxo-1,4-dihydroquinolin-7-yl)oxy]heptyl}-1-methylpiperidinium bromide, R-146224, is a potent, specific ileum apical sodium-dependent bile acid transporter (ASBT) inhibitor; concentrations required for 50% inhibition of [3H]taurocholate uptake in human ASBT-expressing HEK-293 cells and hamster ileum tissues were 0.023 and 0.73 microM, respectively. In bile-fistula rats, biliary and urinary excretion 48 h after 10 mg/kg [14C]R-146224, were 1.49+/-1.75% and 0.14+/-0.05%, respectively, demonstrating extremely low absorption. In hamsters, R-146224 dose-dependently reduced gallbladder bile [3H]taurocholate uptake (ED50: 2.8 mg/kg). In basal diet-fed hamsters, 14-day 30-100 mg/kg R-146224 dose-dependently reduced serum total cholesterol (approximately 40%), high density lipoprotein (HDL) cholesterol (approximately 37%), non-HDL cholesterols (approximately 20%), and phospholipids (approximately 20%), without affecting serum triglycerides, associated with reduced free and esterified liver cholesterol contents. In normocholesterolemic cynomolgus monkeys, R-146224 specifically reduced non-HDL cholesterol. In human ileum specimens, R-146224 dose-dependently inhibited [3H]taurocholate uptake. Potent non-systemic ASBT inhibitor R-146224 decreases bile acid reabsorption by inhibiting the ileal bile acid active transport system, resulting in hypolipidemic activity.     

Characterization of the role of ABCG2 as a bile acid transporter in liver and placenta

ABCG2 is involved in epithelial transport/barrier functions. Here, we have investigated its ability to transport bile acids in liver and placenta. Cholylglycylamido fluorescein (CGamF) was exported by WIF-B9/R cells, which do not express the bile salt export pump (BSEP). Sensitivity to typical inhibitors suggested that CGamF export was mainly mediated by ABCG2. In Chinese hamster ovary (CHO cells), coexpression of rat Oatp1a1 and human ABCG2 enhanced the uptake and efflux, respectively, of CGamF, cholic acid (CA), glycoCA (GCA), tauroCA, and taurolithocholic acid-3-sulfate. The ability of ABCG2 to export these bile acids was confirmed by microinjecting them together with inulin in Xenopus laevis oocytes expressing this pump. ABCG2-mediated bile acid transport was inhibited by estradiol 17β-d-glucuronide and fumitremorgin C. Placental barrier for bile acids accounted for <2-fold increase in fetal cholanemia despite >14-fold increased maternal cholanemia induced by obstructive cholestasis in pregnant rats. In rat placenta, the expression of Abcg2, which was much higher than that of Bsep, was not affected by short-term cholestasis. In pregnant rats, fumitremorgin C did not affect uptake/secretion of GCA by the liver but inhibited its fetal-maternal transfer. Compared with wild-type mice, obstructive cholestasis in pregnant Abcg2(-/-) knockout mice induced similar bile acid accumulation in maternal serum but higher accumulation in placenta, fetal serum, and liver. In conclusion, ABCG2 is able to transport bile acids. The importance of this function depends on the relative expression in the same epithelium of other bile acid exporters. Thus, ABCG2 may play a key role in bile acid transport in placenta, as BSEP does in liver.     

Modulation of bile acids induced by paraquat in rabbits

Rabbit bile was examined for changes in composition induced by paraquat. Paraquat was administered intraperitoneally and changes in bile components were monitored by high performance liquid chromatography. Alterations in the ratios of total glycine/taurine conjugated bile acids (TGC/TTC), cholic acid/deoxycholic acid (CA/DC), cholic acid/chenodeoxycholic acid (CA/CDC) and cholic acid/cholesterol (CA/CH) were measured as an index of paraquat toxicity. A statistically significant increase in the ratio of TGC/TTC was observed, while CA/DC, CA/CDC and CA/CH showed a decrease. Phospholipids, protein, sugar, bilirubin, beta-carotene, vitamin A and vitamin E in the bile and serum of the experimental animals were also monitored. In bile, the levels of cholesterol, phospholipids, protein, sugar, and total bile acids increased while the levels of the antioxidants beta-carotene, vitamin A and vitamin E decreased. A decrease in the bilirubin content of the bile was also observed. These modifications may be useful clinically for assessment of paraquat toxicity.     

Bile acid-binding activity of dodeca-N-methyl neomycin hexamethochloride and dimethylaminopropyl neomycin.

The effect of neomycin and polybasic neomycin derivatives on mixed micellar solutions of bile salt, cholesterol, oleic acid and glyceryl mono-oleate was studied in vitro. Neomycin and its polybasic derivatives caused precipitation of bile salt, fatty acid and cholesterol. Precipitation was more complete with taurochenodeoxycholate micelles than with taurocholate micelles. Dimethylaminopropyl neomycin was the most active compound, followed in order of decreasing activity by neomycin, dodeca-N-methyl neomycin hexamethochloride and N-methylated neomycin. Hexa-N-acetyl neomycin failed to precipitate any of the micellar components. The same order of activity was found when these compounds were tested for hypocholesterolemic activity in newborn chicks fed either a diet without added cholesterol or a diet with 0.25% exogenous cholesterol. The hypocholesterolemic effect in chicks correlated with a 2-5-fold increase of fecal excretion of bile salts, fatty acids and cholesterol. Dimethylaminopropyl neomycin and N-methylated neomycin significantly inhibited the rise of liver cholesterol levels in mice fed a 1% cholesterol-0.1% cholic acid diet. Neither compound was active when given to mice fed a diet without added cholesterol or a diet with 1% cholesterol but without cholic acid.     

The effect of etofibrate on cholesterol and bile acid metabolism in the hamster

Hamsters were given etofibrate at a dose of 300 mg/kg body wt, by gavage for 5 days, while being fed a chow diet. After treatment, serum cholesterol levels were 27% lower compared to those of the control animals. A similar trend was observed for triglyceride levels. Hepatic lipid levels were unchanged by the treatment. HMG-CoA reductase and acylCoA cholesterol acyltransferase were decreased while cholesterol 7 alpha-hydroxylase was not significantly modified by etofibrate. A choleretic effect and an increase of cholesterol excretion into hepatic bile was observed in treated animals. Nevertheless, composition and cholesterol saturation index of gallbladder bile were similar in control and treated animals. With respect to controls, hepatic bile of treated hamsters contained a lesser amount of cholic and deoxycholic acid and a greater amount of ursodeoxycholic acid.     

Hypocholesterolemic effect of bile acid sulfonate analogs in hamsters

We studied the effects of bile acid sulfonate analogs, namely, 3alpha,7alpha,12alpha-trihydroxy-5beta-cholane-24-sulfonate (C-sul), 3alpha,7alpha-dihydroxy-5beta-cholane-24-sulfonate (CDC-sul), and 3alpha,7beta-dihydroxy-5beta-cholane-24-sulfonate (UDC-sul), on serum and liver cholesterol levels, cholesterol 7alpha-hydroxylase activity, and biliary bile acid composition in hamsters fed cholesterol. Of the three analogs studied, UDC-sul slightly but significantly decreased free, esterified, and total cholesterol concentrations in the serum. UDC-sul and CDC-sul reduced liver total cholesterol levels by 25% and 18%, respectively, particularly in the esterified cholesterol fraction. Analysis of biliary bile acids showed the presence of the administered analogs, indicating that sulfonate analogs efficiently participate in enterohepatic cycling. The proportion of cholic acid was increased in all groups fed sulfonate analogs, but the ratio of glycine to taurine conjugated bile acids (G/T) was elevated only in UDC-sul feeding hamsters. There was no significant change in cholesterol 7alpha-hydroxylase activity in hamsters fed C-sul or CDC-sul, while UDC-sul slightly stimulated the enzyme activity compared to the control. The UDC-sul induced decrease in serum and liver cholesterol concentrations may be secondary to enhanced bile acid synthesis. This is supported by the increased cholesterol 7alpha-hydroxylase activity and elevated G/T ratio in biliary bile acids observed following UDC-sul administration.     

Auranofin inhibits the active uptake of bile acid by rat ileum

Auranofin in the mucosal fluid inhibited the active Na+-dependent absorption of taurocholic acid by everted sacs of rat ileum. It did not however, affect the passive uptake of taurocholic acid by sacs of mid-intestine. The inhibition by auranofin of active bile acid absorption could result from its previously demonstrated ability to inhibit Na+, K+-ATPase activity. A reduction in the reabsorption of bile acids by the ileum may contribute to the diarrhoea experienced by some patients taking auranofin.     

Taurine ameliorates cholesterol metabolism by stimulating bile acid production in high‐cholesterol‐fed rats

This study was designed to investigate the effects of dietary taurine on cholesterol metabolism in high‐cholesterol‐fed rats. Male Sprague‐Dawley rats were randomly divided into two dietary groups (n = 6 in each group): a high‐cholesterol diet containing 0.5% cholesterol and 0.15% sodium cholate, and a high‐cholesterol diet with 5% (w/w) taurine. The experimental diets were given for 2 weeks. Taurine supplementation reduced the serum and hepatic cholesterol levels by 37% and 32%, respectively. Faecal excretion of bile acids was significantly increased in taurine‐treated rats, compared with untreated rats. Biliary bile acid concentrations were also increased by taurine. Taurine supplementation increased taurine‐conjugated bile acids by 61% and decreased glycine‐conjugated bile acids by 53%, resulting in a significant decrease in the glycine/taurine (G/T) ratio. Among the taurine‐conjugated bile acids, cholic acid and deoxycholic acid were significantly increased. In the liver, taurine supplementation increased the mRNA expression and enzymatic activity of hepatic cholesterol 7α‐hydroxylase (CYP7A1), the rate‐limiting enzyme for bile acid synthesis, by three‐ and two‐fold, respectively. Taurine also decreased the enzymatic activity of acyl‐CoA:cholesterol acyltransferase (ACAT) and microsomal triglyceride transfer protein (MTP). These observations suggest that taurine supplementation increases the synthesis and excretion of taurine‐conjugated bile acids and stimulates the catabolism of cholesterol to bile acid by elevating the expression and activity of CYP7A1. This may reduce cholesterol esterification and lipoprotein assembly for very low density lipoprotein (VLDL) secretion, leading to reductions in the serum and hepatic cholesterol levels.     

Characterization of the interaction between muscarinic M2 receptors and beta-adrenoceptor subtypes in guinea-pig isolated ileum.

1. Contraction of guinea-pig ileum to muscarinic agonists is mediated by M3 receptors, even though they account for only 30% of the total muscarinic receptor population. The aim of this study was to characterize the biochemical and functional effects of stimulation of the predominant M2 muscarinic receptor (70%) and to investigate the hypothesis that M2 receptors specifically oppose beta-adrenoceptor-mediated effects in the ileum. 2. In guinea-pig ileal longitudinal smooth muscle slices, isoprenaline, a non-selective beta-adrenoceptor agonist, and BRL 37344 (sodium-4-[2-[2-hydroxy-2-(3- chlorophenyl)ethylamino]propyl]-phenoxyacetate sesquihydrate), a beta 3-adrenoceptor selective agonist, increased cyclic AMP accumulation with -log EC50 values of 6.6 +/- 0.1 and 5.8 +/- 0.1 respectively. Maximal stimulation by BRL 37344 (10 microM) was 26.4 +/- 5.2% of that observed with isoprenaline (10 microM). Isoprenaline (10 microM)-stimulated cyclic AMP accumulation was significantly, but not completely, inhibited by propranolol (5 microM), with a propranolol-resistant component of 28.2 +/- 6.8% of the maximal stimulation to isoprenaline. In contrast, basal and BRL 37344 responses were resistant to this antagonist. These data provide evidence that both beta 1- and beta 3-adrenoceptors activate adenylyl cyclase in guinea-pig ileum. 3. Isoprenaline (10 microM)-stimulated cyclic AMP accumulation was inhibited (67.4 +/- 0.9%) by the muscarinic agonist (+)-cis-dioxolane (-log EC50 = 7.3 +/- 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Preparation and Characterization of Reconstructed Small Intestinal Brush Border Membranes for Surface Plasmon Resonance Analysis

PURPOSE: To prepare the surface generated by small intestinal brush border membrane vesicles (BBMVs) for the surface plasmon resonance (SPR) analysis, which allows the real-time measurement of binding events occurring on the intestinal membrane. METHODS: BBMVs were isolated from Sprague-Dawley rats, suspended in HEPES-buffered saline, and flowed over the surface of a SPR sensor chip composed of dextran derivatives modified with lipophilic residues. The surface coverage was determined from binding of bovine serum albumin to BBMV-immobilized sensor chip. The performance of BBMVs immobilized was evaluated by their interaction with otilonium bromide and bile salts. RESULTS: The stable BBMV surface was achieved when BBMV suspension was flowed over the sensor chip for 8 h at a rate of 2 microl/min. The flow of otilonium bromide resulted in an increased SPR signal because of its binding to calcium channel, which is known to be distributed over the gastrointestinal tact. When bile salts were flowed over ileal and duodenal BBMV surfaces, respectively, a slightly higher SPR signal was observed in the ileal BBMV surface, indicating the specific interaction of bile salts with bile acid transporters. CONCLUSIONS: BBMV surfaces may be useful for the estimation of binding events on the intestinal membrane by SPR analysis, especially for the drugs that are orally administrated.     

Antibody-mediated inhibition of fibroblast growth factor 19 results in increased bile acids synthesis and ileal malabsorption of bile acids in cynomolgus monkeys

Fibroblast growth factor 19 (FGF19) represses cholesterol 7α-hydroxylase (Cyp7α1) and inhibits bile acid synthesis in vitro and in vivo. Previous studies have shown that anti-FGF19 antibody treatment reduces growth of colon tumor xenografts and prevents hepatocellular carcinomas in FGF19 transgenic mice and thus may be a useful cancer target. In a repeat dose safety study in cynomolgus monkeys, anti-FGF19 treatment (3-100 mg/kg) demonstrated dose-related liver toxicity accompanied by severe diarrhea and low food consumption. The mechanism of anti-FGF19 toxicity was investigated using in vitro and in vivo approaches. Our results show that anti-FGF19 antibody had no direct cytotoxic effect on monkey hepatocytes. Anti-FGF19 increased Cyp7α1, as expected, but also increased bile acid efflux transporter gene (bile salt export pump, multidrug resistant protein 2 [MRP2], and MRP3) expression and reduced sodium taurocholate cotransporting polypeptide and organic anion transporter 2 expression in liver tissues from treated monkeys and in primary hepatocytes. In addition, anti-FGF19 treatment increased solute transporter gene (ileal bile acid-binding protein, organic solute transporter α [OST-α], and OST-β) expression in ileal tissues from treated monkeys but not in Caco-2 cells. However, deoxycholic acid (a secondary bile acid) increased expression of FGF19 and these solute transporter genes in Caco-2 cells. Gas chromatography-mass spectrometry analysis of monkey feces showed an increase in total bile acids and cholic acid derivatives. These findings suggest that high doses of anti-FGF19 increase Cyp7α1 expression and bile acid synthesis and alter the expression of bile transporters in the liver resulting in enhanced bile acid efflux and reduced uptake. Increased bile acids alter expression of solute transporters in the ileum causing diarrhea and the enhanced enterohepatic recirculation of bile acids leading to liver toxicity.     

Bile Acid Transporters: Structure,Function, Regulation and Pathophysiological Implications

Specific transporters expressed in the liver and the intestine, play a critical role in driving the enterohepatic circulation of bile acids. By preserving a circulating pool of bile acids, an important factor influencing bile flow, these transporters are involved in maintaining bile acid and cholesterol homeostasis. Enterohepatic circulation of bile acids is fundamentally composed of two major processes: secretion from the liver and absorption from the intestine. In the hepatocytes, the vectorial transport of bile acids from blood to bile is ensured by Na⁺ taurocholate co-transporting peptide (NTCP) and organic anion transport polypeptides (OATPs). After binding to a cytosolic bile acid binding protein, bile acids are secreted into the canaliculus via ATP-dependent bile salt excretory pump (BSEP) and multi drug resistant proteins (MRPs). Bile acids are then delivered to the intestinal lumen through bile ducts where they emulsify dietary lipids and cholesterol to facilitate their absorption. Intestinal epithelial cells reabsorb the majority of the secreted bile acids through the apical sodium dependent bile acid transporter (ASBT) and sodium independent organic anion transporting peptide (OATPs). Cytosolic ileal bile acid binding protein (IBABP) mediates the transcellular movement of bile acids to the basolateral membrane across which they exit the cells via organic solute transporters (OST). An essential role of bile acid transporters is evident from the pathology associated with their genetic disruption or dysregulation of their function. Malfunctioning of hepatic and intestinal bile acid transporters is implicated in the pathophysiology of cholestatic liver disease and the depletion of circulating pool of bile acids, respectively. Extensive efforts have been recently made to enhance our understanding of the structure, function and regulation of the bile acid transporters and exploring new potential therapeutics to treat bile acid or cholesterol related diseases. This review will highlight current knowledge about structure, function and molecular characterization of bile acid transporters and discuss the implications of their defects in various hepatic and intestinal disorders.     

Comparison of the choleretic properties of bile acids

The choleretic properties of cholic, chenodeoxycholic, and deoxycholic acid and their taurine and glycine conjugates were compared to their ability to form micelles. It has previously been concluded that deoxycholate has the lowest critical micellar concentration; chenodeoxycholate is slightly higher and cholic is much higher. Conjugation with glycine and taurine has little or no effect on the critical micelle concentration. Since the choleretic properties of bile salts are thought to be directly proportional to their osmotic activities, one might suspect that deoxycholic acid would be the least choleretic, chenodeoxycholic slightly more choleretic and cholic much more choleretic, with little difference between the conjugated and unconjugated forms. However, in the present study, cholic, chenodeoxycholic and taurocholic acid produced similar increases in bile flow (450–700 μl/kg) after an equimolar dose (55 μM/kg). Except for the conjugation of deoxycholic acid with taurine, conjugation of these bile acids with glycine or taurine always decreased the choleretic properties of the bile acids. Therefore, it has been concluded that there is not a good correlation between the in vitro osmotic properties of bile acids and their ability to increase bile flow.     

Bile acid sequestrants based on cationic dextran hydrogel microspheres. 2. Influence of the length of alkyl substituents at the amino groups of the sorbents on the sorption of bile salts

Cationic dextran hydrogel microspheres with pendant quaternary ammonium groups having alkyl substituents (C(2)-C(12)) at quaternary nitrogen were synthesized. The in vitro sorption of sodium salts of four bile acids (glycocholic, cholic, taurocholic, and deoxycholic acids) with these hydrogels was studied as a function of substituent alkyl chain length and bile acid hydrophobicity. Sorption experiments were performed in phosphate buffer solutions (pH 7.4) containing one bile salt (individual sorption) or mixtures of several bile salts (competitive sorption). Parameters for individual sorption were calculated taking into consideration the stoichiometric and cooperative binding of bile salts to oppositely charged polymer hydrogels. The results show that the increase in the length of the alkyl chain of the substituent leads to an increase in both ionization constant K(0) and overall stability constant of binding K, but decreases the cooperativity parameter u. The competitive sorption studies indicate that the hydrogels display a good affinity for both dihydroxylic and trihydroxylic bile salts. The molar ratio of maximum amounts bound for the two types of bile acid is 2 to 1, which is much lower than those reported for other cationic polymers recommended as bile acid sequestrants. The binding constants for the sorption of bile salts by some dextran hydrogels are 20-30 times higher than those obtained for cholestyramine under similar sorption conditions.     

Lack of intestinal transport of [3H]-demethylphalloin: Comparative studies with phallotoxins and bile acids on isolated small intestinal cells and ileal brush border membrane vesicles

Summary Several earlier studies suggested that the uptake of phallotoxins by liver cells is a carrier mediated process using a transport system normally handling bile acids (see Frimmer 1982). In this study we have shown whether ileal cells, well known to transport bile acids too, are able to take up phallotoxins. Isolated epithelial cells prepared from guinea pig ileum accumulated [¹⁴C]-cholate, whereas [³H]-demethylphalloin ([³H]-DMP) was not taken up. The same observation was made with isolated jejunal cells but the uptake of [¹⁴C]-cholate was much slower. [³H]-DMP, however, was partly bound to intestinal cells. This process was not inhibited by cholate, iodipamide, oligomycin and carbonylcyano-chlorophenylhydrazone (CCCP), compounds known to decrease the uptake of phallotoxins into liver cells. Substituting Na⁺ for choline⁺ and also Cl^– for SCN^– did not influence the binding of [³H]-DMP. Frozen intestinal cells from the guinea pig bound two times more [³H]-DMP after thawing compared with intact cells. Supplementary uptake experiments on isolated brush border membrane vesicles from rat ileum revealed that phalloidin does not inhibit taurocholate uptake and that taurocholate does not interfer with [³H]-DMP binding.The results suggest that [³H]-demethylphalloin is not recognized by the bile acid carrier of the guinea pig and the rat ileum. It is concluded that the transport system for bile acids present in ileal cells is different from that of liver cells.Abbreviations TC taurocholic acid - DMP demethylphalloin - CCCP carbonylcyano-chlorophenylhydrazone - EGTA ethylene-glycol-bis-(2-aminoethylether)-N,N-tetraacetic acid - FCCP carbonylcyano-p-trifluoromethoxyphenylhydrazine This work was supported by the Deutsche Forschungsgemeinschaft     

Uptake of bile acids by isolated rat hepatocytes

Hepatic uptake of five common bile acids was examined in isolated rat hepatocytes. Taurocholic acid (TCA), glycocholic acid (GCA), cholic acid (CA), deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA) were studied. Uptake was extremely rapid and was linear for at least 45 sec for all bile acids tested at substrate concentrations from 1 to 400 μM. Both nonsaturable binding to the cell surface membrane and the initial rate of uptake (V₀) of the dihydroxy bile acids (DCA and CDCA) were about ten times greater than those of the trihydroxy bile acids (TCA, GCA and CA) which correlates with the higher lipophilicity of the dihydroxy bile acids. Kinetic analysis demonstrated that uptake of these bile acids was due both to a saturable process and a linear process. The apparent diffusion constant (D_app) of the unsaturable process for the dihydroxy bile acids was also ten times greater than that for the trihydroxy bile acids. After correction for the nonsaturable binding to the cell membrane and linear entry, the K_m and V_max for the uptake was determined. Conjugation with taurine decreased the K_m of CA but not the V_max, while glycine conjugation did not alter either parameter, suggesting that conjugation with taurine may increase its affinity for the transport system. The trihydroxy bile acids have a higher affinity but a lower transporting capacity for the saturable process than the dihydroxy bile acids. In vivo hepatic extraction appears to be more dependent on the affinity of the bile acid for the transport system than the capacity at which it can be transported.     

Budesonide treatment is associated with increased bile acid absorption in collagenous colitis

BACKGROUND: Bile acid malabsorption is frequent in collagenous colitis and harmful bile acids may play a pathophysiological role. Glucocorticoids increase ileal bile acid transport. Budesonide have its main effect in the terminal ileum. AIMS: To evaluate whether the symptomatic effect of budesonide is linked to increased uptake of bile acids. METHODS: Patients with collagenous colitis were treated with budesonide 9 mg daily for 12 weeks. Prior to and after 8 weeks of treatment, the (75)SeHCAT test, an indirect test for the active uptake of bile acid-s, measurements of serum 7alpha-hydroxy-4-cholesten-3-one, an indicator of hepatic bile acid synthesis, and registration of symptoms were performed. RESULTS: The median (75)SeHCAT retention increased from 18% to 35% (P < 0.001, n = 25) approaching the values of healthy controls (38%). The 7alpha-hydroxy-4-cholesten-3-one values decreased significantly among those with initially high synthesis (from 36 to 23 ng/mL, P = 0.04, n = 9); however, for the whole group the values were not altered (19 ng/mL vs. 13 ng/mL, P = 0.23, N.S., n = 19). CONCLUSION: The normalization of the (75)SeHCAT test and the reduction of bile acid synthesis in patients with initially high synthetic rate, suggests that the effect of budesonide in collagenous colitis may be in part due to decreased bile acid load on the colon.