Bile Salt Species Research Articles

Stimulatory and inhibitory effects of bile salts on rat pancreatic secretion

The effects of various species of bile salts (chenodeoxycholate, deoxycholate, ursodeoxycholate and cholate, and their taurine and glycine conjugates) on pancreatic exocrine secretion were studied in conscious rats with external bile and pancreatic fistulae. For examination of the stimulatory effects of bile salts, bile and pancreatic juice were collected for a basal period of 90 minutes and returned to the intestine, and then solutions of bile salts (60 mmol/ L) were infused intraduodenally at a rate of 1 mL/h for 2 hours. For examination of their inhibitory effects, pancreatic secretion was stimulated by exclusion of the bile and pancreatic juice; and then solutions of the bile salts were again infused intraduodenally. Chenodeoxycholate, glycochenodeoxycholate, ursodeoxycholate, deoxycholate, and its conjugates (glycodeoxycholate and taurodeoxycholate) significantly increased the fluid, bicarbonate and protein outputs, and bicarbonate concentration, with decrease in protein concentration. These increases were partially inhibited by infusion of either a cholecystokinin antagonist or secretin antibody. In contrast, cholate, taurocholate, tauroursodeoxycholate, glycoursodeoxycholate, and taurochenodeoxycholate inhibited pancreatic secretion and increase in the plasma cholecystokinin concentration produced by exclusion of bile and pancreatic juice. Thus, some bile salts, including taurocholate and taurochenodeoxycholate (major bile salts in rat bile) inhibited pancreatic secretion and cholecystokinin release, whereas some other bile salts increased pancreatic secretion via cholecystokinin release and secretin release.

Biliary Response to Glucagon in Humans

Glucagon has been demonstrated to have profound effect on biliary secretion in several species. Glucagon's biliary effects were studied in humans following biliary tract surgery. Nine patients underwent common bile duct exploration and insertion of a balloon-occludable t tube. An aliquot of the collected sample was kept and the enterohepatic circulation was maintained by reinfusion of the collected bile via the distal t-tube port. Glucagon increased bile flow and decreased cholesterol and phospholipid output during stable bile acid output. Furthermore high-performance liquid chromatographic analysis of bile acid profiles revealed no significant changes in bile salt species or conjugation after glucagon infusion. Glucagon is probably important in the physiologic regulation of biliary secretion in humans.

Effects of bile salt supplementation on biliary secretion in estrogen-treated rats

The aim of the present study was to determine whether bile acid feeding to rats can reverse ethinyl estradiol-induced cholestasis. Animals received ethinyl estradiol (2 mg/kg/day) for 6 days or were coinfused with estrogen plus various bile acids (60 mg/kg/day). Cholestasis could be significantly prevented by tauroursodeoxycholic acid, was partly corrected by ursodeoxycholic acid, and was unchanged by chenodeoxycholic acid. Total bile salt secretion was increased in every group. The secretion of the major primary bile acids (cholic acid and β-muricholic acid) was restored to a large extent in rats supplemented with tauroursodeoxycholate but not in chenodeoxycholate-fed rats. In the former group, the canalicular transport of taurocholate and the bile salt pool size were identical with those of control rats. The hydrophilic-hydrophobic balance of the administered bile salt species appears to be an essential factor in the restoration of bile secretion, the more hydrophilic bile salt having the more hepatoprotective effect.

Cholesterol monohydrate dissolution rates and solubilities in aqueous taurocholate, taurochenodeoxycholate, and tauroursodeoxycholate solutions: A comparative study

A comparative study of the cholesterol monohydrate (ChM) dissolution rates ( J A ) and solubilities ( C ChM S ) has been carried out in aqueous solutions of taurocholate (TC), taurochenodeoxycholate (TCDC), and tauroursodeoxycholate (TUDC) over a wide range of bile salt (BS) concentrations (from 20 to 120 m M) and at three added sodium chloride levels, 0, 0.2, and 0.4 M. After correcting for total sodium ion concentration, the initial dissolution rate and the rate constant ( k S) obtained in static disk experiments were found to be bile salt species dependent and varied in the order TCDC > TC ⪢ TUDC at low Na + and bile salt concentrations. However, at high Na + and bile salt concentrations, the order changed to TC ⩾ TCDC ⪢ TUDC. Furthermore, the bile salt concentration dependence of J A values was nonlinear and showed a negative curvature for TCDC and TUDC at bile salt concentrations above 40 m M, but was more linear for TC. The C ChM S values were also found to be dependent on bile salt species, Na +, and bile salt concentrations. Their ranking and different curvature closely paralleled those of J A values. The C ChM S data were analyzed in terms of the solubilization ratio ( n ChM: n BS) in order to account for the contrasting ChM solubilization behaviors and capacities observed for the three bile salts over the investigated range of Na + and bile salt concentrations. At saturation, all three bile salts have fewer than one cholesterol per micelle. The much poorer ChM solubilization capacity of TUDC than that of the other bile salts is consistent with the view that the β orientation of its 7-OH group reduces the effective hydrophobicity of the micellar surface and thereby decreases the surface adsorption of cholesterol. It is further suggested that the dependence of ChM solubilization ratio on bile salt concentration and added NaCl may reflect subtle changes in the size and surface structure of the micelles (primary-secondary micelle formation) associated with these variables. The close parallelism between the J A and the C ChM S values leads to nearly identical values for the resistance to dissolution ( R) at constant Na + and bile salt concentrations for the three taurine-conjugated bile salts. On the basis of static disk dissolution rate studies made in the presence of benzalkonium chloride (BC) and additional rotating disk experiments, it was concluded that the relative constancy of R comes primarily from the resistance of the crystal-solution interface rather than from the micellar diffusion across the aqueous boundary layer. Regarding the physical nature of the interfacial barrier, the present study reconfirms our previous finding that the electrostatic repulsion between negatively charged micelles and a negatively charged crystal surface plays a key role. However, we do not rule out contributions from other possible nonelectrical mechanisms. The results of the present study strongly support the hypothesis that the rate-determining step in the interfacial kinetics of ChM dissolution in the three taurine-conjugated bile salt solutions involves the collision complex mechanism rather than a free solute mechanism.

Chiral separation of optical isomeric drugs using micellar electrokinetic chromatography and bile salts

AbstractSeparation of optical isomeric drugs using micellar electrokinetic chromatography and bile salts as surfactants was studied. Optical isomers of diltiazem hydrochloride, trimetoquinol hydrochloride, and other drugs were separated successfully using chiral bile salts under neutral or alkaline conditions. Capacity factors were determined from the migration times of the solute, the micelle, and methanol. The effects of bile salt species or structures and of the pH value of the buffer solution were investigated. A possible chiral separation mechanism is suggested.

Differences in the release of cholesterol from taurocholate versus taurochenodeoxycholate micellar solutions

The maximal micellar solubility, distribution and apparent monomer activity of cholesterol in taurine-conjugated cholate and chenodeoxycholate micellar solutions were studied to clarify the different modulating effect of these bile salt species on cholesterol uptake in an intestinal lumen. The maximal micellar solubility was significantly greater in taurochenodeoxycholate. The intermicellar cholesterol monomer concentration was not significantly different between the two kinds of micellar solution. However, the apparent cholesterol monomer activity determined using an artificial organic phase (polyethylene disc) was significantly higher in taurocholate than that in taurochenodeoxycholate. A linear relationship between the intermicellar cholesterol concentration and the apparent cholesterol monomer activity was found, with the slope depending upon the bile salt species. It is concluded that the difference in partitioning of cholesterol from taurocholate and taurochenodeoxycholate micelles into a fixed organic phase may contribute in part to the different regulating effects of these bile salts on the uptake of cholesterol in the intraluminal phase.

Self-association of human apolipoproteins A-I and A-II and interactions of apolipoprotein A-I with bile salts: quasi-elastic light scattering studies.

We employed quasi-elastic light scattering (QLS) to systematically study the aqueous self-association of human apolipoproteins A-I and A-II (apo A-I and apo A-II) and the interactions of apo A-I with common taurine-conjugated bile salts. Self-association of apo A-I was promoted by increases in apolipoprotein concentration (0.09-2.2 mg/mL) and ionic strength (0.15-2.0 M NaCl), inhibited by increases in temperature (5-50 degrees C) and guanidine hydrochloride concentration (0-2.0 M), and unaffected by hydrostatic pressures up to 500 atm. The mean hydrodynamic radius (Rh) of apo A-I micelles ranged from 38 A to a maximum asymptotic value of 68 A. We examined several possible models of apo A-I self-association; the model that best fitted the Rh values assumed that apo A-I monomers first interacted at low concentrations to form dimers, which then further associated to form ring-shaped limiting octamers. Comparison of the temperature-dependent and ionic strength dependent free energy changes for the formation of octamers from apo A-I dimers suggested that hydrophobic forces strongly favored self-association and that electrostatic repulsive forces were only weakly counteractive. Apo A-II self-association was also promoted by increases in apolipoprotein concentration (0.2-1.8 mg/mL) and inhibited by increases in guanidine hydrochloride concentration (0-1.0 M) but was unaffected by variations in temperature (10-37 degrees C): the largest Rh values observed were consistent with limiting tetramers. As demonstrated by equilibrium dialysis, bile salts in concentrations below their critical micellar concentrations (cmc) bound to apo A-I micelles but had no effect upon apo A-I self-association, as inferred from constant Rh values. When bile salt concentrations exceeded their aqueous cmc values, a dissociation of apo A-I micelles resulted with the formation of mixed bile salt/apo A-I micelles. These studies support the concepts that apo A-I and apo A-II form small dimeric micelles at low concentrations that grow sharply to reach limiting sizes over a narrow concentration range. The influences of bile salt concentration and species upon these micelles have relevance to the plasma transport of bile salts in high-density lipoproteins and to the physical-chemical state of apo A-I and apo A-II molecules in native biles.

Effects of bile salts on bile formation in rabbits

The effects of different species of bile salts: deoxycholate, taurochenodeoxycholate, ursodeoxycholate, glycodeoxycholate, tauroursodeoxycholate, chenodeoxycholate and cholate (DCA, TCDC, UDCA, GDCA, TUDC, CDCA, CA) on bile secretion were examined in anesthetized rabbits using two different infusion routes. When bile salts were infused intravenously, all bile salts (except for TCDC) significantly increased the volume of bile and bile salt excretion, but their respective efficiency for bile formation was different. The concentration of bicarbonate ion in the bile significantly increased during the choleretic periods induced by DCA, UDCA, GDCA and CDCA but remained unchanged with the other bile salts (CA, TCDC, TUDC). In rabbits, where a bile salt solution was infused in the duodenum and then drained from the intestine through an incision in the distal part of duodenum, none of these bile salts affected bile secretion. The effects of intravenously administered bile salts on rabbit bile secretion are different in terms of their choleretic potency and bicarbonate excretion depending on the species of bile salts used. Furthermore, it was concluded that the intraduodenal infusion of UDCA, which was found to stimulate the pancreatic exocrine function (1), did not affect bile secretion.

Effects of bile salts on pancreatic secretion in rabbits: ursodeoxycholate infused into the duodenum stimulates pancreas.

The effects of six species of bile salts, deoxycholate, ursodeoxycholate, glycodeoxycholate, tauroursodeoxycholate, chenodeoxycholate, and cholate (DCA, UDCA, GDC, TUDC, CDCA, CA), on pancreatic secretion were examined in anesthetized rabbits. When bile salts were infused intraduodenally, only UDCA significantly increased the pancreatic juice flow and bicarbonate output, whereas the increase in protein output was only transient. In contrast, UDCA infused intravenously did not affect the pancreatic secretion. Furthermore, none of the other bile salts, either intraduodenally or intravenously administered, had any significant effect on pancreatic exocrine function. Pancreatic responses to the intraduodenally administered UDCA in terms of fluid, bicarbonate, and protein secretion were similar to those of secretin infused intravenously. Thus, it was suggested that UDCA infused intraduodenally stimulates pancreatic secretion, possibly via the release of a secretin-like substance(s) from the duodenal wall.

Aqueous bile salt-lecithin-cholesterol systems: equilibrium aspects.

Cholesterol is solubilized by bile salt and bile salt-lecithin micelles without appreciable alteration in preexisting micellar size or structure. In dilute (approximately 3 gm per dl) model bile, but not in concentrated (approximately 10 gm per dl) systems, supramicellar concentrations of cholesterol are also solubilized in "stable" microdispersions of small lecithin-cholesterol vesicles (approximately 200 to 400 A in radius). Under physical-chemical conditions of physiological importance, the micellar solubilities of cholesterol are influenced by the total lipid concentrations, lecithin-to-bile salt ratio and bile salt species. The hydrophilic-hydrophobic balance of the bile salt monomer also influences the number and composition of precipitate phases coexisting in equilibrium with saturated micelles. When diluted below the critical micellar concentration (more correctly, the intermicellar concentration) of the bile salt species, the systems no longer contain micelles, but cholesterol remains dispersed in unilamellar liposomes that form spontaneously from the mixed micellar concentrations of the biliary lipids.

Bile salt structure and phase equilibria in aqueous bile salt and bile salt-lecithin systems.

The hydrophilic-hydrophobic balance of bile salt monomers can be readily quantified by their elution sequence during reverse-phase high-performance liquid chromatography. Such studies have demonstrated that subtle variations in bile salt structure have profound effects on the hydrophilic-hydrophobic balance of this important family of detergent-like molecules. The common trihydroxy bile salt, cholate, is more hydrophilic than dihydroxy bile salts with alpha-oriented OH groups. In contrast, dihydroxy bile salts with one equatorial OH function are more hydrophilic than cholate. Hydrophilic bile salts have, in general, higher critical micellar concentrations than do hydrophobic bile salts and their primary micelles polymerize less readily to form secondary micelles either with increasing bile salt concentrations or with increases in ionic strength. Hydrophilic bile salts also disperse lecithin into mixed micelles at a slower rate than do hydrophobic bile salts. The structure of mixed bile salt-lecithin micelles is more complex than previously believed and varies with bile salt-to-lecithin ratio. These micelles are disc-like in which bile salts saturate the lecithin bilayer "core" presumably as reverse micelles, as well as coating the perimeter as a bilayered "ribbon". The ratio of bile salt to lecithin in the bilayer and the intermicellar monomeric bile salt concentration (critical micellar concentration) determines the macroscopic phase limit. With the common bile salt species, the lecithin-to-bile salt phase limit does not correlate closely with the hydrophilic-hydrophobic balance of the bile salt monomers.(ABSTRACT TRUNCATED AT 250 WORDS)

Mixed micelle properties and intestinal cholesterol uptake

The solubilizing powers of taurocholate, taurochenodeoxycholate and tauroursodeoxycholate for monoolein and cholesterol, and the size of the bile salt-monoolein-cholesterol micelles have been determined. For the three bile salt species, the micellar size depends on the saturation with monoolein. As a result, for a given bile salt to monoolein ratio, the taurochenodeoxycholate micelles are smaller than those of taurocholate and both are smaller than those of tauroursodeoxycholate. Intestinal cholesterol uptake has been studied in vitro as a function of the micellar size and the saturation degree with cholesterol. For a given bile salt to monoolein ration and 1) for low cholesterol concentrations, taurocholate leads to the greatest rates of uptake ; 2) for high cholesterol content, taurochenodeoxycholate induces the largest uptake. The specific micellar characteristics of the tauroursodeoxycholate micelles clearly demonstrate why this bile salt is of so little help in the intestinal uptake of cholesterol.

Comparative effects of cholic, chenodeoxycholic, and ursodeoxycholic acids on micellar solubilization and intestinal absorption of cholesterol

Cholesterol absorption was studied in mice receiving cholic, chenodeoxycholic, or ursodeoxycholic acids (0.2% of the diet) for 2 months. Cholesterol absorption was greater with cholic acid (79%) than with chenodeoxycholic acid feeding (60%) and the lowest levels were observed during ursodeoxycholic acid feeding (37%). Under the three diets, bile acid pool and bile acid secretion were not different. Biliary cholesterol secretion was increased by cholic acid. The bile acid fed represents at least 80% of total bile acids. Micellar solubilization of oleic acid and cholesterol in the presence of each tauro-conjugated bile salt (10 mM) was determined in vitro by the coprecipitation method. Whatever the pH conditions, taurochenodeoxycholate solubilized significantly more cholesterol and more oleic acid than taurocholate. Tauroursodeoxycholate had the poorest detergent properties for both lipids. The differences between the three bile salts for cholesterol solubilization were enlarged by lowering pH and by high oleic acid concentration. Therefore the decrease in cholesterol absorption observed during ursodeoxycholic acid feeding could be explained by the poor detergent properties of this bile salt species. On the other hand, there is no relationship between the detergent properties of taurochenodeoxycholate and taurocholate and their effects on cholesterol absorption in mice. These results suggest that, in this particular case, micellar solubilization is not the rate limiting step in cholesterol absorption.

The physical chemistry of cholesterol solubility in bile. Relationship to gallstone formation and dissolution in man.

We determined the maximum solubilities of cholesterol in aqueous conjugated bile salt-egg lecithin-cholesterol systems as a function of several physical-chemical variables including those of physiological importance employing phase equilibria techniques. Equilibration rates are influenced by time and the method of sample preparation in that metastable supersaturation is readily induced at high bile salt: lecithin ratios, and equilibrium saturation by dissolution is achieved sluggisly at low bile salt:lecithin ratios. Equilibrium values for cholesterol saturation vary with the bile salt species, bile salt: lecithin ratio, temperature, ionic strength, and, in particular, with the total concentration of biliary lipids. Within physiological bile salt:lecithin ratios at 37 degreesC the influence of bile salt type and ionic strength is small, whereas the effects of bile salt:lecithin ratio and the total lipid concentration are major factors. We plotted on triangular coordinates a family of cholesterol solubility curves for each total lipid concentration (0.30--30 g/dl) and computed fifth-degree polynomial equations for each curve. With both the curves and the polynomial equations the "per cent cholesterol saturation" of fasting gallbladder and hepatic biles from patients with and without gallstones was calculated and both methods gave similar values. These results deomonstrate that by employing cholesterol saturation values appropriate to the total lipid concentration (range 0.2--24.9 g/dl) of individual biles, all cholesterol stone patients have supersaturated gallbladder biles, (mean, 132% [normal weight individuals], and 199% [morbidly obese individuals]). With controls and pigment stone patients the mean values were 95 and 98%, respectively, and in both approximately 50% of biles were supersaturated. Fasting hepatic biles were significantly more supersaturated than gallbladder biles (means 228--273%). Cholesterol monohydrate crystals were found in the majority of gallbladder (83%) and hepatic (58%) biles of cholesterol gallstone patients but were not observed in pigment stone patients or controls. We conclude that of the several factors in addition to the bile salt:lecithin ratios which can influence the cholesterol saturation of bile the total lipid concentration is the predominant determinant physiologically. Our results demonstrate that (a) metastable supersaturation is frequent in both normal and abnormal biles, (b) cholesterol gallstone patients have supersaturated gallbladder and hepatic biles without exception, and (c) the predominant driving force for cholesterol precipitation appears to be the absolute degree of cholesterol supersaturation.

Solubility of cholesterol in bile salt-lecithin model systems.

Cholesterol solubility was determined in model systems of unconjugated and conjugated bile salts and lecithin at physiologic concentrations. Conjugated bile salts had somewhat less dissolving power than unconjugated forms, with taurine conjugates showing less power than glycine conjugates. Lecithin increased the dissolving power of each bile salt species proportionally up to a lecithin-bile salt molar ratio of 1.0, at which point the amount of cholesterol dissolved was triple that in the absence of lecithin. At most physiologic ratios of lecithin-bile salt, however, lecithin only doubles the amount of cholesterol dissolved. Lecithin reduces, but does not eliminate, significant differences in the cholesterol dissolving power of both unconjugated and conjugated bile salt species. Mixtures of unconjugated bile salts show a simple additive effect in the absence of lecithin, but when lecithin is present the dissolving power of deoxycholate predominates over cholate, and of cholate over chenodeoxycholate. Mixtures of conjugated bile salt species produce a simple additive effect on dissolving power in both the presence and the absence of lecithin. Our cholesterol saturation curves for glycodeoxycholate and glycocholate at a total bile salt concentration of 150 mM, which we consider representative of the cholesterol dissolving power of human gallbladder bile, showed less dissolving power at lecithin-bile salt ratios of 0.25 to 0.50 than did the curve of Adminrand and Small; our curves were reasonably similar to those of Hegardt and Dam on the trilinear graph. Our studies show that changes in total bile salt concentration encountered in human gallbladder bile do produce significant shifts in the saturation curve.