[Interrelationship of reflux bile acid concentration and the gastric mucosal change with reference to the pathophysiologic significance of taurine conjugated deoxycholic acid and chenodeoxycholic acid]

Since chronic gastritis is adversely affected by reflux bile acids, we are interested in which of these bile acids cause the most damage to the gastric mucosa as ulcerogenic factors in the stomach. We examined 34 patients suffering from the peptic ulcers, and have assumed that taurine conjugated deoxycholic acid (TDC) and chenodeoxycholic acid (TCDC) may act as the mst ulcerogenic factors. Moreover TCDC was suggested to be associated with the cystic dilatation of the gastric gland. It was also suggested that TDC is involved in the increased frequency of intestinal metaplasia as a factor backgrounding cancer.

Adsorption of mixtures of bile salt taurine conjugates to lecithin-cholesterol membranes: implications for bile salt toxicity and cytoprotection

Tauroursodeoxycholate (TUDC), a relatively hydrophilic bile salt, reduces disruption of cholesterol-rich membranes by more hydrophobic bile salts such as taurocholate (TC), taurochenodeoxycholate (TCDC), or taurodeoxycholate (TDC). We examined the interactions of these bile salts in adsorption to large unilamellar vesicles to determine whether TUDC may stabilize membranes by preventing adsorption of more toxic bile salts. Fractional adsorption was quantified by rapid ultrafiltration. Adsorption coefficient Ai was defined for each bile salt i as ([bound i]/[free i])/[lecithin]. Affinity of different bile salts for lecithin vesicles varied with their relative hydrophobicity, increasing in the order TUDC < TC << TCDC < or = TDC. Ai of each bile salt fell with its accumulation on membranes, reaching a minimum at bound bile salt/lecithin mole ratio (B:L) between 0.05 and 0.1, then increasing with formation of higher-affinity mixed micelles. Inclusion of cholesterol in vesicles reduced Ai of all bile salts. In heterologous binding studies at submicellar concentrations, Ai of each bile salt varied with total B:L but was independent of the specific bile salts present on the membrane. Addition of TUDC to TDC reduced binding of TDC to membranes only slightly and lowered the threshold TDC concentration associated with transition to mixed micelles. However, above this threshold, TUDC markedly altered the adsorption of TDC to lecithin-containing phases. We conclude that TUDC does not directly stabilize membranes; rather, reduced permeabilization and dissolution of cholesterol-rich membranes after addition of TUDC to TDC may result from effects on the formation and structure of simple and mixed micelles.

Molecular and functional characterization of an organic anion transporting polypeptide cloned from human liver

BACKGROUND & AIMS

Based on a recently cloned rat liver organic anion transporter, we attempted to clone the corresponding human liver organic anion transporting polypeptide.

METHODS

A human liver complementary DNA library was screened with a specific rat liver complementary DNA probe. The human liver transporter was cloned by homology with the rat protein and functionally characterized in Xenopus laevis oocytes.

RESULTS

The cloned human liver organic anion transporting polypeptide consists of 670 amino acids and shows a 67% amino acid identity with the corresponding rat liver protein. Injection of in vitro transcribed complementary RNA into frog oocytes resulted in the expression of sodium-independent uptake of [35S]bromosulfophthalein (Michaelis constant [Km], approximately 20 mumol/L), [3H]cholate (Km, approximately 93 mumol/L), [3H]taurocholate (Km, approximately 60 mumol/L), [14C]glycocholate, [3H]taurochenodeoxycholate, and [3H]tauroursodeoxycholate (Km, approximately 19 mumol/L). Northern blot analysis showed cross-reactivity with messenger RNA species from human liver, brain, lung, kidney, and testes. Polymerase chain reaction analysis of genomic DNA from a panel of human-rodent somatic cell hybrids mapped the cloned human organic anion transporter to chromosome 12.

CONCLUSIONS

These studies show that the cloned human liver organic anion transporter is closely related to, but probably not identical to, the previously cloned rat liver transporter. Furthermore, its additional localization in a variety of extrahepatic tissues suggests that it plays a fundamental role in overall transepithelial organic anion transport of the human body.

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

Bile acid processing in the long-term, bile duct obstructed rat liver was studied ex vivo. Twenty four and 72 h, respectively, after bile duct obstruction the isolated liver was perfused with taurodeoxycholate (16 nmol/min per g liver) the bile duct still being closed. Uptake, metabolism and regurgitation profile were traced by bolus injection of tritium-labeled bile acid; in addition, concurrent histological changes were examined by light- and electron microscopy. Ligation caused dilatation of the intrahepatic ductular branches and increased the serum bile acid concentration to 740 +/- 75 microM (controls: 16 +/- 2.12), reaching its maximum within 24 h. At 16 nmol/min per g liver uptake rate was > 96% in controls and in bile duct obstructed rats. Maximal uptake rates (assessed separately) differed between controls and bile duct obstructed rats (700 nmol/min per g liver vs. 460). Controls excreted more than 80% of labeled bile acid in bile within 10 min after bolus injection. Biliary recovery of label was virtually completed after 30 min. In bile duct obstructed rats excretion of label back to the perfusate effluent (regurgitation) started quantitatively 5 min after bolus application and peaked between 10 and 40 min; after 80 min, effluent recovery was incomplete (about 60% of bolus injected). Biliary bile acids of controls consisted of about 20% taurodeoxycholate-metabolites; bile acids in the perfusate effluent of bile duct obstructed rats of about 55%. The major metabolite in all animal groups was taurocholate; minor metabolites were tauroursocholate, tauro-3 alpha,7 = 0,12 alpha-cholanoic acid and 3-sulfo-taurodeoxycholate. Histologically, inflammation and periportal edema were present after 1 day of bile duct obstruction. After 3 days, marked proliferation of bile ductules was the dominant histological feature. It is concluded that during initial bile duct obstruction, bile acid processing is not altered, although ultrastructural alterations occur early.

Effect of deoxycholate on immunoglobulin G concentration in bile: studies in humans and pigs

Because an increase in biliary deoxycholate levels seems to be a risk factor for cholesterol gallstone formation, we determined the relationship between deoxycholate levels and levels of the pronucleating protein, immunoglobulin G (Ig) in human gallbladder bile. Patients with cholesterol gallstones had a higher concentration of biliary IgG compared with a pigmented stone group and control patients. This was associated with the simultaneous presence of two conditions in the cholesterol stone group, supersaturated bile and a high deoxycholate/cholate ratio. The other patient groups met only one of the two conditions. Next, animal studies were performed to determine if model biles mimicking the two conditions could affect IgG secretion by the gallbladder. Gallbladders were exposed in vivo and then in an Ussing chamber to model biles. The voltage clamp technique was used to monitor functional integrity of the preparation. Three different model biles were tested: (1) taurodeoxycholate (TDC), 80%; taurocholate (TC), 20%; and cholesterol saturation index (CSI), 1.2; (2) TDC, 20%; TC, 80%; and CSI, 1.2; and (3) TDC, 80%; TC, 20%; and CSI, 0.6. IgG concentrations became significantly higher in group 1 than in the other two groups. The concentration of mucous glycoprotein was also significantly greater in group 1 when compared with group 2. Plasma cells were increased in number in mucosal and submucosal layers in group 1. We conclude that cholesterol supersaturated model bile with high content of TDC induces gallbladder epithelial alterations, which increase the luminal concentration of IgG and mucous glycoprotein.

Changes in bile acid composition of serum and gallbladder bile in bile duct ligated dogs

Biliary obstruction was produced by surgical ligation of the common bile duct to observe alterations in serum bile acid composition. The percent composition of serum bile acids was found to change with time. Taurocholic acid increased on day 3 and accounted for more than 90% of the total bile acids in all dogs, however it decreased after day 7. The percentage of taurochenodeoxycholic acid (TCDC) and taurodeoxycholic acid (TDC) decreased to 4.2-6.0% and 0.2-0.7% on day 3, respectively. However, the percentage of TCDC increased after day 7 in all dogs and reached greater than 20% on day 14 in 2 dogs, whereas the percent TDC after bile duct ligation remained low in all dogs. Glycolithocholic acid, which was not identified in normal dog sera, was detected on day 3 and remained throughout the study in all dogs. Bile acid composition of gallbladder bile sampled on day 35 was similar to the serum bile acid composition on the same day. This indicates that the bile acids refluxed into the circulation in these dogs. In the present study, total cholic acid to chenodeoxycholic acid (C:CDC) ratio increased to 15.5-22.3 at three days post bile duct ligation and after the day 14, the C:CDC ratio decreased to its pre-ligation value or below. In contrast, the glycine conjugated to taurine conjugated bile acids (G:T) ratio did not change. Therefore, at this time, the G:T ratio would not be usable as an indicator of liver disease in dogs while it may be possible to use the C:CDC ratio.

Interaction of lysophospholipid/taurodeoxycholate submicellar aggregates with phospholipid bilayers

The equilibrium partitioning and the rate of transfer of monoacylphosphatidylethanolamines (lysoPEs) between phospholipid bilayers and lysoPE/taurodeoxycholate submicellar aggregates (SMAs) were examined with a series of environment-sensitive fluorescent-labeled N-(7-nitro-2,1,3-benzoxadiazol-4-yl)-1-monoacylphosphatidyletha nolamine (N-NBD-lysoPE) probes of differing acyl chain length. Our previous work has demonstrated the formation of SMAs between bile salts and lysophospholipids [Shoemaker & Nichols (1990) Biochemistry 29, 5837-5842]. The experiments in the current work demonstrate that SMAs can coexist with phospholipid vesicles and can function as shuttle carriers for the transfer of lysophospholipids between membranes. The formation of submicellar aggregates of N-NBD-lysoPE and taurodeoxycholate (TDC) in equilibrium with 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) vesicles was determined from the increase in fluorescence generated upon addition of TDC to POPC vesicles containing 3 mol% N-NBD-lysoPE and 3 mol% N-(lissamine rhodamine B sulfonyl)dioleoylphosphatidylethanolamine (N-Rh-PE) as a nonextractable fluorescence energy-transfer quencher. The fraction of lysolipid extracted increased as a function of decreasing acyl chain length of the N-NBD-lysoPE molecule. The half-time for equilibration was independent of acyl chain length and averaged 44 ms at 10 degrees C. The delivery of N-NBD-lysoPE from preformed N-NBD-lysoPE/TDC SMAs into POPC vesicles containing the energy-transfer quencher N-Rh-PE was measured by the rate of fluorescence decline. The initial rate of insertion increased with decreasing acyl chain length of the N-NBD-lysoPE molecule and as a function of vesicle concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of basic cholane derivatives on intestinal cholic acid metabolism: in vitro and in vivo activity

A representative series of hydroxy-5 beta-cholanyl-24-amines were tested both in vitro and in vivo with respect to their activity against the intestinal bacteria responsible for bile acid metabolism. For the in vitro studies, radiolabeled [14C]cholic acid was incubated with human stools both in aerobic and anaerobic conditions in the presence of the title compounds at a dose of 10 micrograms/mL, and the biotransformation of cholic acid into radiolabeled deoxycholic acid and other metabolites was followed by TLC-radiochromatography. Of the compounds studied, 3 alpha, 12 alpha-dihydroxy-5 beta-cholan-24-N-methylamine showed the highest activity. This compound was used for the in vivo studies and was shown to inhibit the formation of endogenous secondary bile acids when chronically administered to rats at a dose of 60 micrograms/day for 15 days. The treated rats showed an increased ratio of taurocholic acid (primary bile acid) to taurodeoxycholic acid (secondary bile acid) in bile, a fact further suggesting a potent antibacterial activity of the compound toward bacteria responsible for bile acid metabolism.

Proton magnetic resonance studies of the aggregation of taurine-conjugated bile salts

The concentration dependence of the 500 MHz 1H-NMR spectra of taurocholate, taurochenodeoxycholate, taurodeoxycholate, and the monosulfate esters of taurochenodeoxycholate has been examined at 0.154 M NaCl in D2O. The resonances of the C18, C19, and C21 methyl groups and the C23 methylene group are differentially broadened with respect to the C25 and C26 methylene and C7 (or C12) methine groups with increasing bile salt concentration for each of the bile salts studied. These data confirm hydrophobic association and indicate that the side chain contributes to the hydrophobic surface of the bile salt. The chemical shift difference of the anisochronous C23 methylene protons is different in monomer and aggregate form. The C25 methylene protons are isochronous in monomeric form but anisochronous in aggregate form. The concentration dependence of the observed chemical shifts has been analyzed to estimate the critical concentration associated with the onset of these changes. The conformer population about the C22-C23 bond changes before the anisochronicity of the C25 methylene protons develops. This indicates that the C23 methylene group is affected by the initial stages of self-association, whereas specific motional constraints about the N-C25 bond in the taurine moiety are only induced in large primary micelles. The difference in the chemical shift of the C25 methylene protons depends on the structure of the bile salt. The relative magnitude of the shift differences is not altered by the presence of phosphatidylcholine. The data suggest that in primary micelles or mixed micelles the taurine moiety conforms to segregate the hydrophilic groups of the bile salt and effects greater van der Waals' contact between the hydrophobic surfaces.

Calcium binding by monosulfate esters of taurochenodeoxycholate

The effect of sulfate esterification of the 3 alpha- or 7 alpha-hydroxyl groups of taurochenodeoxycholate on calcium binding was studied at 0.154 M NaCl in the presence and absence of phosphatidylcholine using a calcium electrode. For comparison, similar studies were made with taurochenodeoxycholate, taurodeoxycholate, and taurocholate. No high affinity calcium binding was demonstrable for any of these bile salts in pre-micellar solutions. Taurine-conjugated bile salts have greater affinity for calcium when in a micellar form. At elevated bile salt concentrations, the calcium binding of unsulfated dihydroxy taurine conjugates was similar to that of the monosulfate esters of taurochenodeoxycholate. The presence of phosphatidylcholine decreased calcium binding of the unsulfated dihydroxy bile salts and slightly increased calcium binding by taurocholate. However, the addition of phosphatidylcholine to monosulfate esters of taurochenodeoxycholate results in large increments in calcium binding. The results indicate that increased calcium binding due to the presence of phosphatidylcholine in bile salt solutions depends, in part, on the hydrophilicity of the bile salt and that the interaction of monosulfate esters of taurochenodeoxycholate with phosphatidylcholine leads to the formation of a high affinity calcium binding site.

Function of rat hepatocyte tight junctions: studies with bile acid infusions

To determine the effects of alteration of biliary paracellular permeability on bile flow and composition, we measured the biliary outputs of compounds highly concentrated in bile, all infused at a constant rate in the isolated rat liver perfused with Krebs-Henseleit buffer in a one-pass fashion. Paracellular permeability was increased by infusing 10(-8) M vasopressin (VP). The cholephilic compounds were three cations of various molecular weights, tributylmethylammonium (TBuMA), N-acetylprocainamide ethobromide (APAEB), and propidium iodide, and two anions, taurocholate (TC), a micelle-forming bile acid, and taurodehydrocholate (TDHC), an nonmicelle former. When TC was infused and paracellular permeability increased with VP, neither bile flow nor TC output changed, whereas outputs of cations fell. When TDHC was infused, TDHC output fell, as did outputs of all cations. The decrements in cation outputs exceeded that of TDHC and were inversely related to the molecular weight of the cation. To document that these changes were not related to reduced uptake of these compounds, we tested the uptakes of TBuMA, APAEB, and TDHC into isolated hepatocytes. In no case did 10(-8) M VP significantly reduce uptake. The data demonstrate that micelle-forming bile acids, with their high effective molecular weights, do not efflux from the biliary tree when permeability is increased with VP, whereas nonmicelle-forming bile acids do. Cations efflux more readily than anions, and within this group efflux rate is inversely related to molecular weight. The data confirm the size and charge selectivity of biliary tree permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Solubilization of multilamellar liposomes of egg yolk lecithin by the bile salt sodiumtaurodeoxycholate and the effect of cholesterol--a rapid-ultrafiltration study

The solubilization of multilamellar egg yolk lecithin liposomes by sodiumtaurodeoxycholate in aqueous phase was studied by ultrafiltration as a function of time, bile salt and cholesterol concentration. The corresponding equilibrium states were analysed. Complete solubilization was achieved at total bile salt/lecithin molar mixing ratios of approximately 5. The minimum ratio to start solubilization was 0.1, corresponding to a free bile salt concentration of only 5% of the critical micelle concentration (CMC). Mean equilibrium constants for the partition of bile salts between non-filterable aggregates and filterable mixed micelles and also the free bile salt concentration were determined. Sodiumtaurodeoxycholate had a higher affinity for small mixed micelles than for lamellar mixed aggregates especially in the presence of cholesterol, which reduces the degree and rate of the solubilization process. A non-homogeneous distribution of bile salts in the lipid phase was detected at low bile salt concentrations.

A new method for purification of Eimeria tenella merozoites

A rapid and simple method for purifying second generation merozoites of Eimeria tenella was developed using a host tissue digestion fluid, containing 0.25% trypsin and 0.5% taurodeoxycholic acid, to liberate merozoites grown in chick embryos or from parasitized ceca. After filtration, the digestion procedure yielded 1.4 x 10(7) or 8.33 x 10(7) merozoites per embryo or cecum, respectively. These yields were nine-fold for embryos and three-fold for ceca in comparison to previous reports. Viability of the merozoites was normal as assessed by their ability to reinfect embryos and cell cultures. The new method has advantages in that large numbers of pure, viable merozoites can be obtained quickly and easily, and the procedures require minimal effort and supplies.

Role of primary and secondary bile acids as feedback inhibitors of bile acid synthesis in the rat in vivo

The effect of various primary and secondary bile acids on the rates of synthesis of all major bile acids was studied in the live rat with an extracorporal bile duct. Bile acid synthesis was determined using HPLC based on mass or by isotope dilution. Derepressed rates of bile acid synthesis (30-54 h) were inhibited by an infusion of taurocholic acid only at a supraphysiological dose of 500 mumol/kg per h, but not at 300 mumol/kg per h, which approximates the initial bile acid secretion (250 mumol/kg per h). When administered together with taurocholic acid (200 mumol/kg per h) only a high dose of taurochenodeoxycholic acid (100 mumol/kg per h) decreased taurocholic but not tauromuricholic or taurochenodeoxycholic acid synthesis. The only bile acid suppressing taurocholic acid (36-71%) and taurochenodeoxycholic acid (up to 33%) formation at an infusion rate close to the normal portal flux was deoxy- or taurodeoxycholic acid at 15-50 mumol/kg per h. It may be concluded that deoxycholic acid and possibly other secondary bile acids are much more potent inhibitors than primary bile acids.

The nature of choleresis induced by deoxycholate and its conjugates in the rabbit

A hypothesis for the mechanism of bile salt-induced choleresis with increased bile bicarbonate concentration (cholehepatic recycling; CHR), requires a relatively high pK'a value of a bile salt to be easily protonated in bile canaliculi. If the choleresis induced by taurodeoxycholate and glycodeoxycholate (which increase bile bicarbonate concentration in rabbits) is to be explained by this thesis, these bile salts must be extensively deconjugated in the liver, enabling a bile salt having a higher pK'a value, free deoxycholate, to undergo CHR. With a stepwise increase in the infusion rate, the increments of bicarbonate concentration, as well as the bile flow rate induced by taurodeoxycholate and glycodeoxycholate, were as efficient as those caused by an equimolar infusion of deoxycholate. With infusion of conjugated deoxycholates, the major bile salts excreted in the bile were those which had been infused. In studies with conjugated deoxycholates, unconjugated deoxycholate was not detectable in the bile. Furthermore, deoxycholate concentration in the liver significantly increased after a 2-h infusion of deoxycholate but did not increase after infusion of either glycodeoxycholate or taurodeoxycholate. The present results suggest that the choleresis induced by conjugated deoxycholates in rabbits requires an explanation other than CHR of deoxycholate.

Role of the hepatic artery in canalicular bile formation by the perfused rat liver. A multiple indicator dilution study

The role of the hepatic artery in tracer water exchange and regulation of permeation of small solutes during canalicular bile formation was studied in the rat using a system that permitted perfusion of both hepatic artery and portal vein. Hepatic vein and biliary multiple indicator dilution curves were obtained after injection of indicators into either vessel. The main difference in hepatic venous dilution curves was a 3.1-fold longer t0 (time spent in nonexchanging vessels) and a 5% larger equivalent water space after injection into the hepatic artery. Biliary tracer recovery of water was markedly higher after arterial injection than after portal vein injection. Both taurocholate and taurodehydrocholate stimulated bile flow and increased biliary tracer recovery after injection into either vessel. The biliary recovery of sucrose relative to that of water, which is a measure of biliary sucrose permeation, was much lower when given into the hepatic artery than when given into the portal vein. During taurocholate infusion, it decreased by 33% in the hepatic artery but increased 36% in the portal vein. Taurodehydrocholate, by contrast, did not affect permeation of sucrose given into the portal vein. Our studies demonstrate marked exchange of tracer water in the biliary epithelium. Taurocholate, but not taurodehydrocholate, increases permeation of sucrose into bile in the portal vein bed while both bile salts decrease it in the arterial bed.

Bile acid binding to dietary casein: a study in vitro and in vivo

1. Studies were carried out in vitro using an ultracentrifugation method to quantify bile acid binding to the different components of a Lundh test meal, and to determine what factors influence bile acid binding to one of the components (casein). We validated the ultracentrifugation method by showing good agreement with the equilibrium dialysis method. Studies were carried out in vivo on jejunal aspirate from 10 ileal resection patients in order to determine whether bile acid binding to casein could be demonstrated, and whether this influenced aqueous-phase bile acid and fatty acid concentrations. 2. In vitro, the Lundh test meal was found to adsorb bile acid. The protein content of the meal (casein) alone accounted for this binding, which was abolished by use of casein hydrolysate. The binding to casein was a saturable process. Both binding affinity and binding capacity were significantly greater for taurocholate at pH 4.5 than at pH 6.5, and for dihydroxylated than for trihydroxylated bile acid, suggesting that hydrophobic bonding was involved. 3. In vivo, jejunal samples aspirated at pH greater than 6 from 10 ileal resection patients showed 25% binding of bile acid to protein. On substitution of amino acids for casein, mean binding was reduced to 16% (P less than 0.05), residual binding being attributed to endogenous protein. This was associated with an increase in fatty acid solubilization from 28% to 60% (P less than 0.025).(ABSTRACT TRUNCATED AT 250 WORDS)

The role of aromatic side chain residues in micelle binding by pancreatic colipase. Fluorescence studies of the porcine and equine proteins

Fluorescence techniques have been employed to study the interaction of porcine and equine colipase with pure taurodeoxycholate and mixed micelles. Nitrotyrosine-55 of porcine colipase is obtained by modification with tetranitromethane (low excess, in the presence of taurodeoxycholate) of the protein followed by gel filtration and ion-exchange chromatography. Verification of the residue modified was obtained by h.p.l.c. peptide purification and sequence analysis. Reduction and quantitative reaction with dansyl chloride yields a fluorescent derivative that is twice as active in conjunction with lipase as is native colipase and that exhibits a strong emission band at 550 nm. Addition of micellar concentrations of taurodeoxycholate causes a 4.3-fold increase in the emission maximum as well as a 70 nm blue shift to 480 nm. Inclusion of oleic acid to form a mixed micelle reduces these spectral effects. Scatchard analysis of the data yield a Kd of 6.8 X 10(-4) M and a single colipase-binding site for taurodeoxycholate micelles. The data, by analogy to a phospholipase system, are consistent with a direct insertion of dansyl-NH-tyrosine-55 into the micelle. The presence of a single tryptophan residue (Trp-52) in equine colipase provides an intrinsic fluorescent probe for studying protein-micelle interaction. The emission maximum of horse colipase at 345 nm indicates a solvent-accessible tryptophan residue which becomes less so on binding of micelles. A blue shift of 8 nm and a 2-fold increase in amplitude is indicative of a more hydrophobic environment for tryptophan induced by taurodeoxycholate micelles. There is also a decrease in KSV for acrylamide quenching in the presence of micelles, which further supports a loss of solvent accessibility. The most dramatic pH effects are observed with KI quenching, and may indicate the presence of negative charges near Trp-52.

Binding of bile salts to fibre-enriched wheat fibre

A commercial product of fibre-enriched wheat fibre (Fiberform R) was tested for its binding of bile salts in vitro. The wheat fibre preparation was standardized and through enzymatic digestion of protein and starch contained 78 per cent fibre (w/w). Fibre-enriched wheat fibre bound with high capacity both conjugated and unconjugated bile salts. Binding was saturable, reversible and showed no specificity towards tauro- or glycine-conjugated bile salts. Binding was rapid, dependent on pH, was enhanced by the presence of high salt concentrations and partially inhibited by 6 M urea. This indicated that binding was a combination of hydrophobic and hydrophilic interactions.

Greater taurodeoxycholate biotransformation during backward perfusion of rat liver

Differing patterns of taurodeoxycholate (TDC) metabolism and biliary excretion were studied with a forward-and-backward perfusion model of the isolated rat liver. Livers were perfused with 8 microM TDC via either the portal vein (forward) or the hepatic vein (backward). Bile was collected, total bile acids measured enzymatically, and bile composition determined by high-pressure liquid chromatography and thin-layer chromatography. During backward perfusion 48% of infused TDC was metabolized to taurocholate (TC) and 22.0% to other minor TDC metabolites. During forward perfusion, however, only 16% of administered TDC was metabolized to TC and 6.5% to minor metabolites. Total bile acid output was similar for both forward and backward perfusions. The kinetics of biliary bile acid excretion also differed between forward and backward perfusion. The time necessary for 50% excretion of labeled TDC and its metabolites was 3.5 +/- 0.45 min during forward and 18 +/- 3.50 min during backward perfusion, a time difference of 14.5 min. The greater biotransformation of TDC during backward perfusion could be explained by its longer intracellular residence. The reason for the delayed excretion of TDC during backward perfusion is unknown.

Trypsin activation of porcine procolipase. Kinetics of activation and effects on lipid binding

The kinetics of trypsin activation of pancreatic procolipase was investigated and the pH dependence of the binding of procolipase and colipase to a tributyrine-bile salt interface studied. The Km was 0.06 mM and kcat 8 s-1, and was of the same order of magnitude as for the activation of pancreatic zymogens. At basic pH values colipase had a higher affinity for the tributyrine-bile salt interface as compared to procolipase. The trypsin activation of procolipase ensures a rapid degradation of dietary lipids in the intestine.

Bile acid metabolism during development: metabolism of taurodeoxycholic acid in human fetal liver

The metabolism of tauro-[24-14C]deoxycholic acid was studied in microsomal preparations from fetal liver. The livers were obtained at legal abortions performed between week 13 and 24. Taurodeoxycholic acid was efficiently hydroxylated in the 1 beta- and 7 alpha-positions. The hydroxylase activities did not increase with gestational age. A marked variation in extent of hydroxylation was noted between different preparations. The results are discussed in relation to earlier knowledge of fetal and neonatal bile acid metabolism.

Concentrations of glycine- and taurine-conjugated bile acids in portal and systemic venous serum in man

Concentrations of glycine and taurine conjugates of cholic, chenodeoxycholic, and deoxycholic acid in portal and systemic venous serum and in bile were measured in eight subjects undergoing elective cholecystectomy. Mean concentrations in systemic serum ranged from 0.07 to 0.17 mumol/l, in portal serum from 0.49 to 2.09 mumol/l, and in bile from 2.72 to 17.2 mmol/l. The percentage content of trihydroxy-bile acid conjugates in bile (49%) and in portal serum (51%) was higher than in systemic serum (35%) (P less than 0.001). The estimated hepatic fractional uptake of glycocholic acid (mean, 83%) and of taurocholic acid (83%) was higher than the uptakes of the dihydroxy-bile acid conjugates (60-68%). The percentage contents of glycine-conjugated bile acids in systemic serum (mean, 66%), portal serum (62%), and bile (65%) were not significantly different.

Intestinal absorption of dl-alpha-tocopherol from bile salts and polysorbate 80 micellar solutions in rat

The intestinal absorption of dl-alpha-tocopherol (VE) from various micellar solutions was studied by the in situ recirculating perfusion in rat small intestine. The perfused micellar solutions of VE were formed by sodium taurocholate (STC), sodium taurodeoxycholate (STDC) or polysorbate 80 (PS-80). The absorption ratio of VE was STC greater than STDC greater than PS-80 micellar solutions. The addition of egg lecithin (PC) to all micellar solutions caused the decrease of the absorption. The absorption ratio did not necessarily have a simple correlation with the VE solubilization in these micellar solutions. And it was also found that the absorption ratio correlated with the micellar size and with net water flux in the intestinal lumen.

Role of bile salts and trypsin in the pathogenesis of experimental alkaline esophagitis

The pathogenesis of alkaline reflux esophagitis was investigated in an experimental model by assessing individually the influence of different bile salt moieties and trypsin on esophageal mucosa. An isolated segment of rabbit esophagus was perfused at pH 7 with a solution containing the test agent under study, and the severity of mucosal damage was assessed by using as indicators of mucosal integrity transmucosal potential difference, net flux of Na+, and mucosal permeability to two neutral molecules of different sizes, 3H-H2O and 14C-erythritol. The data indicate that the secondary dihydroxy bile salt, deoxycholate, in its deconjugated form was highly injurious to esophageal mucosa; it was the only test agent that caused gross mucosal lesions during the experiment. The respective conjugated bile salt moiety, taurodeoxycholate, had a weaker effect. Also the primary dihydroxy bile salt, chenodeoxycholate, in its deconjugated form caused moderate damage to the mucosa, whereas its conjugated form, taurochenodeoxycholate, had no effect. The effect of the other three bile salts tested--cholate, taurocholate, and taurolithocholate--was negligible. Trypsin also adversely affected the mucosa, but its effect was weaker than that of deoxycholate. The results suggest that the deconjugated bile salts deoxycholate and chenodeoxycholate (which are formed following bacterial colonization of the upper gastrointestinal tract in the absence of gastric acid), the conjugated bile salt taurodeoxycholate, and the proteolytic enzyme trypsin may have significant roles in the pathogenesis of alkaline reflux esophagitis.