Bile Salt Solutions Research Articles

Studies on Bile Salt Solutions. Part 2. Acid Catalyzed Hydrolysis of Trimethyl Orthobenzoate in Solutions of Glycine and Taurine Conjugated Bile Salts

Abstract The reactivity of trimethyl or thobenzoate has been studied, at 310.5 K, in solutions of the glycine and taurine conjugates of the cholanic acids. The rate-concentration profiles are characterized by peaks and troughs which coincide with discontinuities in the slopes of the surface tension-concentration profiles.

Studies in bile salt solutions: 1. Surface tension evidence for a stepwise aggregation model

Measurement has been made of the surface tension, at 310.5 K, of solutions of sodium cholate, deoxycholate, chenodeoxycholate, dehydrocholate, and lithocholate at pH 7.00 in 0.01 mole dm −3 phosphate buffer; and of solutions of sodium glycocholate at pH values of 5.47, 4.90, and 4.07, of sodium glycodeoxycholate and glycochenodeoxycholate at pH values of 4.77 and 4.37, respectively, and of sodium taurocholate, taurodeoxycholate, and taurochenodeoxycholate at pH 4.09, all in 0.03 mole dm −3 acetate buffer. Values of the critical micelle concentration, CMC, have been determined. The surface tension plots for the taurine and glycine conjugates show discontinuities which have been discussed in terms of the phase separation and stepwise association models of aggregation.

The binding of micellar lipids to chitosan.

The lipid binding capacity of chitosan (partially deacetylated chitin) was determinined with respect to micellar solutions of bile salts, dodecyl sulfate, natural ox bile and an artificial mixed microemulsion. The stoichiometry was determined following the separation of the solid phase by filtration or centrifugation. The major variables in the extent of binding were the pH and ionic strength, suggesting that the interactions are mainly of ionic nature. It is noteworthy that under optimal conditions chitosan could bind, i.e., coprecipitate, with 4-5 times of its weight with all the lipid aggregates tested. These results have a bearing on the nutritional and pharmacological applications of chitosan. The analyses of the components from the precipitates with microemulsion and ox bile show a significant selectivily of binding caused by hydrophobic interactions.

In Vitro Interaction of 7,12-Dimethylbenz[<italic>a</italic>]anthracene and Its Biliary Metabolites With Dietary Fibers<xref ref-type="fn" rid="FN2">2</xref>

This in vitro study examined the ability of various dietary fiber components to bind 7,12-dimethylbenz[a]anthracene (DMBA), a hydrocarbon carcinogen known to contaminate food. Bile salt solutions of DMBA were incubated with individual fiber materials under various conditions, and the degree of binding was assessed. Binding of DMBA from simple bile salt solution was greatest with delipidated bran greater than acid lignin greater than alpha-cellulose greater than unprocessed bran. Binding to acid lignin was slowly reversible, was constant within the pH range 4-8, and appeared independent of a bile salt-fiber interaction. Acid lignin bound DMBA from a mixed lipid-bile salt solution significantly, but less effectively than from pure bile salt solutions. DMBA biliary metabolites from Sprague-Dawley rats were bound less extensively to all the fiber materials than was the parent hydrocarbon, but following hydrolysis of the metabolites by beta-glucuronidase binding was significantly increased. These results indicate that there is considerable potential for dietary fiber to interact with DMBA and its metabolites in the lumen of the gastrointestinal tract, possibly influencing hydrocarbon carcinogen bioavailability.

Bile absorption occurs during disruption of the esophageal mucosal barrier

The role of bile salt absorption in bile-induced disruption of the esophageal mucosal barrier was determined using the continuously perfused rabbit esophagus model. Mucosal barrier disruption was determined by measuring net flux of hydrogen ion, potassium, and glucose. Bile salt absorption was measured by determining net flux of radiolabeled bile salt solution using liquid scintillation counting. Bile salt-containing solutions were prepared with varying concentrations of two bile salts, taurocholate and deoxycholate. The pH of the bile salt exposure also was varied to vary the extent of mucosal injury. The results show that changes in bile salt concentration and in pH of exposure were associated with significant differences in both extent of mucosal barrier disruption and bile salt absorption. Bile salt absorption was associated by direct linear correlation with each index of mucosal barrier function studied. These findings suggest that bile salt absorption plays a role in bile-induced disruption of the esophageal mucosal barrier.

Static and dynamic light scattering studies of micellar growth and interactions in bile salt solutions

of the metal is bare again and the oxidation process can go on until the whole metal has been destroyed. Once again the oxidative dissolution of metal particles by treatment with NO points out the powerful ability of NO for desintering supported metals. The oxidation by O2 is more difficult. For sample reduced at 200 C a very long time in O2 at 200 C is needed for recovering the previously ionic state of nickel. But for the sample treated at 500 C under H2, reoxidation is limited. Even heated at 500 C the metal cannot be completely converted into ions. This probably occurs because at elevated temperature nickel cannot be prevented from sintering and large particles are formed as shown by magnetic measurements. Moreover it cannot be excluded that oxygen reacts with metal particles forming nonvolatile surface oxide deposited onto the metallic phase. So oxidation would be inhibited.

The “Mirroring” of Gallstones. Description of a Novel Silvering Method to Determine the Surface Area of an Irregular Object

We describe a novel "silvering" method to determine the surface area of nonspherical objects and have applied this method to human cholesterol gallstones. A standard curve is first constructed, using data obtained from the dissolution rates of silver-coated plastic spheres of known dimensions in unstirred thiosulfate-ferricyanide solutions. Silver dissolution rates of silver-coated gallstones are then correlated with the standard curve so that the equivalent spherical surface area of the gallstones may be estimated. The technique has been applied to cholesterol dissolution rates of gallstones from the same patient and from different patients in unstirred bile salt (sodium chenodeoxycholate) solutions. The results demonstrate that cholesterol dissolution rates per unit surface area are identical for small stones as well as large ones, are identical for all stones from the same gallbladder, but are somewhat dissimilar for those originating from different gallbladders. The experimental results are in agreement with a priori theoretical predictions of mass transfer from spherical objects, and correlate satisfactorily with experimental dissolution rates of pure cholesterol monohydrate disks in unstirred bile salt solutions.

Study of the influence of sodium taurocholate (STC) and sodium glycocholate (SGC) on the mass transfer of certain drugs. Digoxin

Digoxin has an aqueous solubility of 1.811 mg/100 ml and a dissolution efficiency of 13.7%. The presence of bile salts raised the solubility to 3.621 and 4.039 mg/100 ml and the dissolution efficiency to 25.7 and 19.3% for STC and SGC, respectively. The relatively low solubility of digoxin compared to other polar drugs points to its non-polar behaviour. The addition of lecithin or cholesterol to bile salt solutions, slightly decreases the solubility and dissolution rate of digoxin, probably due to competition between lecithin and cholesterol and digoxin for the same binding site of bile salt micelles. However, the simultaneous presence of lecithin and cholesterol together with bile salts increases, slightly, the solubility and dissolution rate of digoxin, most probably due to increased volume and hydrophobicity of the core of mixed micelles. Addition of fatty acids to SGC solution does affect but very slightly the solubility and dissolution rate of the drug. The fatty acid lowers, to some extent the solubility of the drug in STC solutions, while the dissolution rate is only slightly affected. Addition of monolaurin to bile salt solutions decreases the solubility of the drug to some extent. However, GM myristate and GM stearate slightly enhance both the solubility and dissolution rate of the drug. The presence of GM laurate slightly lowers the dissolution rate of the drug in STC solutions but not in SGC ones. The influence of GM laurate on the solubility of digoxin seems to be quite comparable to that of lecithin. The simultaneous presence of the investigated additives in STC or SGC systems increases slightly the solubility and dissolution rate of the drug. This has been explained on the basis of increased hydrophobicity and volume of the core of mixed micelles.

Conformational change in pancreatic lipase induced by colipase

Pancreatic lipase is a key enzyme for the intraluminar digestion of fats. The adsorption of lipase to the substrate which occurs readily when the particles are composed of pure triacylglycerol is prevented by the accumulation at the interface of various amphiphiles like bile salt and phospholipids present in the duodenum during fat digestion. In the presence of pancreatic colipase the activity of lipase is, however, fully restored. The exact mechanism for this reactivation is not known. Two different mechanisms have been suggested. The first considers colipase as an ‘anchor’ for lipase at the hydrophilic interface. In a series of sequential steps colipase will alone recognize and bind to the interface and from there bind to lipase thus anchoring the enzyme back to its triacylglycerol substrate [ 1,2]. The other claims that none of the proteins could bind to the interface but that lipase and colipase form a complex with bile-mixed micelles in solution. This complex is then adsorbed as a single unit by virtue of the bile lipids to the triacylglycerate interface 131. Lipase is known to form a 1: 1 molar complex with colipase [4]. The binding which is both electrostatic and hydrophobic has a dissociation constant of 5 x lop7 M in buffer [5]. In bile salt solution the binding is weaker (&l = 3 X 10 -6 M). However, in the presence of mixed oleic acidbile salt micelles the binding is strongly increased [6] with a Kd of lo* M [7]. In the lipase/colipase binding there has been no indication for any conformational change when the interaction has been studied in buffer or in bile salt solution as indicated by CD measurements 14). This may, however, be due to weak binding between the two proteins under these conditions which makes necessary the use of concentrated solutions to assure a binding. Recently, a covalent complex of lipase and colipase was obtained by use of a crosslinking agent [8]. This complex had binding properties to a mixed phospholipid-triacylglycerol interface that could not be explained as an effect of colipase alone but suggested that’colipase had somehow induced a conformational change in lipase enabling lipase to take part in the substrate binding. This study shows that colipase can induce a conformational change in lipase seen as an ultraviolet spectral shift of the complex compared to the single proteins. The change was -5-fold greater in the presence of mixed oleic acid-bile salt micelles. At pH 5, the addition of bile salt to lipase alone also induced a spectral shift. The mechanism for colipase reactivation of lipase is discussed in the light of the above experiments.

Effects of pH, pNa, and temperature on micelle formation and solubilization of cholesterol in aqueous solutions of bile salts

Effects of pH, pNa, and temperature on micelle formation and solubilization of cholesterol in aqueous solutions of bile salts

Surfactant-selective electrode study of bile salt—protein binding

An electrode selective to bile salt anions, has been evaluated for use in bile salt solutions and solutions containing bile salt anions and a protein. The electrode potential values obtained are a direct function of the activities of the corresponding bile salt anions. The electrode potential, follows Nernstian behavior in the premicellar region of bile salt solutions. A minimum is observed in the Nernst plot corresponding to the critical micelle concentration. Results obtained using these electrodes in solutions containing protein and bile salt have been used to construct Scatchard plots for the bile anion-protein binding. The treatment of the data with non-linear least-squares fit gave estimates of the binding constants and the number of binding sites which are comparable to previous results obtained from equilibrium dialysis measurements. Five bile salts studied bound in the following relative order: sodium deoxycholate ∼- sodium chenodeoxycholate > sodium ursodeoxycholate > sodium cholate > sodium dehydrocholate. Binding studies were also carried out as a function of temperature which enabled the estimation of thermodynamic functions of binding. ΔH° of binding is positive suggesting that these biological detergents bind to hydrophobic sites on serum albumin.

The hydrophobic-hydrophilic balance of bile salts. Inverse correlation between reverse-phase high performance liquid chromatographic mobilities and micellar cholesterol-solubilizing capacities.

To examine quantitatively the hydrophobic-hydrophilic properties of bile salts, we determined the reverse-phase high performance liquid chromatographic (HPLC) mobilities of monomeric bile salt solutions and the equilibrium cholesterol-solubilizing capacities of 100 mM micellar solutions. Studies with the common bile salts (ursodeoxycholate, UDC, cholate, C, chenodeoxycholate, CDC, and deoxycholate, DC) demonstrated that HPLC mobility, which correlates with hydrophilicity, was markedly influenced by both position and orientation, in addition to number, of hydroxyl functions, in that mobility decreased in the order UDC > C > CDC > DC. Conjugation of the bile salt was also important, in that the HPLC mobility of the taurine (T)-conjugates was greater than the glycine (G)-conjugates which in turn was greater than that of the free bile salts. Equilibrium micellar cholesterol solubilities were also influenced by bile salt structure and correlated inversely with hydrophilicity, in that solubility decreased in the order DC > CDC > C > UDC with free bile salts > G-conjugates > T conjugates. For each bile salt series, double logarithmic plots of the cholesterol-solubilizing capacities expressed in mole fraction units versus the HPLC retention factors (k') gave linear relationships. Linear regression equations were employed to predict the equilibrium cholesterol-solubilizing capacities of a number of less common bile salts from their HPLC retention factors. Each theoretical value agreed closely with that derived entirely by experiment. A comparison of the HPLC mobilities of the less common bile salts with the more common species revealed that not only were sulfate and oxo substituents more hydrophilic than alpha-oriented hydroxyl functions, but, in the dihydroxy species, a single equatorial hydroxyl function such as in UDC (3alpha,7beta) and in hyodeoxycholate (3alpha,6alpha) was more hydrophilic than two or three hydroxyl functions at 3, 7, and/or 12alpha (axial) positions. These studies taken together suggest that reverse-phase HPLC mobility and equilibrium cholesterol-solubilizing capacities are inverse functions of each other and correlate closely with the hydrophilicity of bile salt molecules. In addition, the evidence here deduced further strengthens our recent deductions based on an evaluation of a number of other physical-chemical properties (Carey, M. C., J-C. Montet, M. C. Phillips, M. J. Armstrong, and N. A. Mazer, 1981. Biochemistry. 20: 3637-3648.) that cholesterol may be solubilized in micellar bile salt solutions by both hydrophobic and hydrophilic association with the external ("hydrophilic") surface of bile salt micelles rather than with the hydrophobic surface of the micelle's interior.-Armstrong, M. J., and M. C. Carey. The hydrophobic-hydrophilic balance of bile salts. Inverse correlation between reverse-phase high performance liquid chromatographic mobilities and micellar cholesterol-solubilizing capacities.

Effects of intestinal secretagogues and distension on small bowel myoelectric activity in fasted and fed conscious dogs.

1. Defined jejunal segments were perfused with solutions of bile salts and of ricinoleic acid during fasting and after feeding in two groups of conscious dogs, one with the segment in continuity, and the other with a Thirty-Vella loop. Myoelectric activity was recorded from chronically implanted electrodes on the jejunal segment and also from the proximal and distal in situ bowel.2. The results in both groups were identical. During fasting, migrating complexes were present in the segment, but were replaced by intermittent spike activity during chenodeoxycholate without and with ricinoleic acid perfusion. After food, when migrating complexes were replaced by intermittent spike activity, none of the solutions produced any consistent effect.3. In fasted animals, low levels of distension (15 mmHg) interrupted the migrating complexes in the segment and induced intermittent spike activity which was similar to that seen with the secretagogues. The migrating complexes in the main bowel continued during distension. In fed animals, spike activity increased in the segment during distension at 25 mmHg and decreased in the main bowel. In both groups, distension of the segment to pressures between 37.5 and 50 mmHg abolished spike activity both in the distended segment and the main bowel in fasted and fed states, and, in fasted dogs, migrating complexes were also abolished.4. These results demonstrate that the inhibitory intestino-intestinal reflex is mediated through extrinsic nerves and does not require an intact myenteric plexus, whereas the altered myoelectric activity induced by secretagogues is a local effect and does not spread to adjacent bowel through either intrinsic or extrinsic neural pathways. It seems likely that the local motor effect of secretagogues is a result of net secretion, producing distension to pressures below the threshold required to activate the intestino-intestinal reflex.

Postprandial intestinal hyperemia: role of bile salts in the ileum

In an autoperfused dog ileum preparation, artificial pressure, venous outflow pressure, blood flow, and arteriovenous oxygen difference were measured while bile and bile salt solutions, at physiological concentrations, were placed in the lumen. Intraluminal placement of endogenous bile, synthetic bile, or bile salt solutions increased ileal blood flow (99 +/- 10, 94 +/- 20, and 104 +/- 17%, respectively) and oxygen uptake (30 +/- 5, 36 +/- 9, and 28 +/- 5%, respectively). Endogenous bile pretreated with cholestyramine, a bile salt-sequestering resin, did not alter ileal blood flow, yet increased ileal oxygen uptake by 11 +/- 3%, a response similar to that observed while Tyrode's solution (the vehicle) was in the lumen. Intra-arterial infusion of bile salts increased ileal blood flow in a dose-dependent manner, while not significantly altering ileal oxygen uptake. The results of the present study indicate that bile salts play an important role in the functional (postprandial) hyperemia in the ileum by 1) directly dilating the ileal vasculature and 2) enhancing ileal metabolism during their active absorption.

Plasma Concentrations of Gastric Inhibitory Polypeptide after Intraduodenal Infusion of Cattle Bile and Synthetic Bile Saits in Man

A solution of 6 g cattle bile infused intraduodenally (no. = 6) increased the plasma GIP concentration from 35.4 (31.4-43.6) to 47.1 (33.9-51.2) pM. Human bile also increased the GIP concentration in a single patient. A solution of bile salts in an amount and concentration comparable to those of human bile did not influence the GIP concentration.

Temperature and concentration effects on the viscoelasticity of concentrated aqueous solutions of bile salts in the ultrasonic range

Measurements of longitudinal ultrasonic absorption in a concentrated aqueous solution of the bile salt sodium deoxycholate at different temperatures enable a better characterization of the exhibited viscoelasticity. An analysis of the data in the viscoelastic region shows that the dynamic shear viscosity follows a temperature and concentration superposition principle and that the volume viscosity is small. Such conclusions support a previously suggested possibility of polymerization of the small "primary" micelles observed at low concentration.

Thermodynamics of aqueous bile salt solutions: Heat capacity, enthalpy and entropy of dilution

Heat capacity data at various temperatures and enthalpies of dilution at 25°C are reported for aqueous bile salt solutions. The apparent molal heat contentsφL have been combined with osmotic and activity coefficients to obtain the excess molal entropies. Measurements of some of these properties have also been carried out with the anionic detergent sodium dodecylsulfate so that the bile salt micellization process may be compared with that of a classical detergent. The observed data have been interpreted in terms of the hydrophobic association properties of bile salts in aqueous solution.

Influence of Desalivation on Acid Secretory Output and Gastric Mucosal Integrity in the Rat

Exogenous administration of substances extracted from rodent salivary glands may increase the resistance of gastric mucosal barrier to the disruptive actions of ulcerogenic agents and/or reduce acid secretory output. In the present study the influence of desalivation in the rat on acid secretory function and mucosal integrity has been investigated. Experiments were performed on rats 4 wk after removal of the major salivary glands and ligation of the salivary ducts. Intravenous infusion of pentagastrin (0.1--0.4 microgram/kg/min) resulted in an increase in acid output in desalivated rats although the responses was less than that observed in sham-operated controls. Intraluminal instillation of a bile salt solution (5 mM in 150 mM HCl) in control animals resulted in a significant loss of H+ and the luminal appearance of Na+ and K+. The net fluxes of Na+ and K+ were exacerbated in the desalivated group. Furthermore, the mean area of bile salt-induced ulceration was significantly greater in desalivated rats than in the control group. In the absence of bile salt treatment there was no difference in either the transmural ionic fluxes or area of ulceration between the two groups. These results suggests that removal of the major salivary glands in rats decreases the resistance of the gastric mucosa to bile salt-induced damage.

Inhibition of human pancreatic lipase-colipase activity by mixed bile salt-phospholipid micelles.

Mixed dihydroxy bile salt-phosphatidylcholine (PC) micelles can inhibit the hydrolysis of gum arabic-stabilized long-chain triglyceride emulsions by 10(-8) to 10(-9) M concentrations of human pancreatic lipase and colipase. Trypsin treatment of this colipase preparation did not reverse the inhibition, suggesting that procolipase, as a possible contaminant, was not the inhibitory factor. Human biliary phospholipid-cholesterol liposomes, isolated by gel filtration and redissolved in bile salt solutions, inhibited lipolysis to the same degree as solutions of bile salt containing purified PC. The degree of inhibition depended principally on the species of bile salt present (e.g., taurochenodeoxycholate greater than taurodeoxycholate greater than tauroursodeoxycholate greater than taurocholate). In the absence of bile salt, PC (0.4 mM) liposomes alone were not inhibitory over the physiological time range studied. Bile salt solutions of phosphatidylethanolamine or sphingomyelin also inhibited lipase activity, whereas those containing oleyl alcohol, oleyl aldehyde, oleic acid, and lyso-PC did not. PC molecules were found to partition between the triglyceride emulsion interface and the bulk aqueous phase. Full reversal of inhibition occurred in the presence of phospholipase A2, which hydrolyzed the phospholipids to lysolecithin and fatty acids. Mixed bile salt-phospholipid micelles caused marked decrease in the binding of lipase and colipase to the triglyceride substrate and displaced the proteins into the aqueous phase. The results taken together suggest that colipase binds to certain bile salt-PC associations independent of whether the aggregates are located at the surface of a triglyceride particle as a monolayer or in the bulk aqueous phase as mixed micelles.

Aqueous lipid phases of relevance to intestinal fat digestion and absorption.

The phase behavior of monoglyceride/water systems, with oleic and linoleic acid as the dominating fatty acid residues, was investigated. Increased solubilization of triglycerides (oil) or oleic acid in the cubic liquid-crystalline phase formed by monoglyceride and water resulted in the formation of a reversed hexagonal liquid-crystalline phase followed by an L2-phase. The liquid-crystalline phases have different dispersion properties compared to each other in dilute micellar bile salt solutions. The cubic phase is found to be easily dispersed. The relevance of aqueous lipid phases other than micellar is discussed in relation to intestinal lipid digestion and absorption.