Tauroursodeoxycholate Research Articles

Bile acids affect liver mitochondrial bioenergetics: possible relevance for cholestasis therapy.

It has been pointed out that intracellular accumulation of bile acids cause hepatocyte injury in cholestatic disease process. This study was aimed to test if cytotoxicity of these compounds is mediated through mitochondria dysfunction. Bile acids effects on isolated rat liver mitochondrial were analyzed by monitoring changes in membrane potential and mitochondrial respiration, as well as alterations in H(+) membrane permeability and mitochondrial permeability transition pore induction. Increasing concentrations of the bile acids litocholic (LCA), deoxycholic (DCA), ursodeoxycholic (UDCA), chenodeoxycholic (CDCA), glycochenodeoxycholic (GCDC), or taurochenodeoxycholic (TCDC) decrease transmembrane potential (delta psi) developed upon succinate energization. These compounds also decreased state 3 respiration and enhanced state 4. We have also demonstrated that the observed concentration-dependent stimulation of state 4 by LCA, DCA, CDCA, TCDC, and GCDC, is associated with an enhanced permeability of mitochondria to H(+). Addition of LCA, DCA, CDCA, TCDC, GCDC, and UDCA to mitochondria energized with succinate resulted in a dose-dependent membrane depolarization and stimulation of mitochondrial permeability transition. Tauroursodeoxycholate (TUDC) elicited no significant effect on succinate-supported mitochondrial bioenergetics. In contrast, in the presence of glycoursodeoxycholic (GUDC), delta psi increases as a function of bile salt concentration. The results of this investigation demonstrate that at toxicologically relevant concentrations, most but not all bile acids alter mitochondrial bioenergetics, so impairment of mitochondrial function can be clinically relevant for patients with cholestasis.

Regulation of multidrug resistance 2 P-glycoprotein expression by bile salts in rats and in primary cultures of rat hepatocytes

Biliary phospholipid secretion is tightly coupled to the secretion of free cholesterol and bile salts. The secretion of phospholipids across the canalicular membrane of hepatocytes occurs via the multidrug resistance 2 (mdr2) P-glycoprotein (Pgp). The mechanism underlying the coupling of bile salt and phospholipid secretion has not been elucidated. The aims of this study were to determine the effects of bile acid structure on the expression of mdr2 in vitro and in vivo. Under optimal culture conditions, taurine-conjugated bile acids (50 μmol/L) increased mdr2 messenger RNA (mRNA) levels in the following order: taurocholate (TCA) (288 ± 36%, P < .005) = taurodeoxycholate (TDCA) (276 ± 36%, P < .025) > taurochenodeoxycholate (TCDCA) (216 ± 34%, P < .025) > tauroursodeoxycholate (TUDCA) (175 ± 28%,P < .05) of control levels. The increase in mdr2 mRNA levels by TCA was both time and concentration dependent. Cholate feeding to rats with intact enterohepatic circulation increased mdr2 transcriptional activity by 4-fold and protein mass by 1.9-fold. Chronic biliary diversion (CBD) decreased mdr2 mRNA levels to 66 ± 9% (P < .025) of sham-operated controls. Intraduodenal infusion of TCA for 48 hours in CBD rats caused a significant increase in mdr2 mRNA levels (224%) as compared with CBD controls. A diet high in cholesterol (4%) decreased mdr2 mRNA levels to 57% ± 2 (P < .001) of pair-fed controls. Squalestatin (1 μmol/L), an inhibitor of cholesterol biosynthesis, increased mdr2 mRNA levels by 8.8-fold (P < .005) in hepatocyte cultures after 24 hours. In conclusion, in the rat, bile acids up-regulated mdr2 transcriptional activity whereas cholesterol decreased mdr2 mRNA both in vitro and in vivo. (Hepatology 2000;32:341-347.)

Hydrophobic Self-Association of Sodium Taurochenodeoxycholate and Tauroursodeoxycholate

The aggregation patterns of sodium taurochenodeoxycholate (TCDC) and tauroursodeoxycholate (TUDC) in an isotonic sodium chloride solution are investigated by frontal chromatography on Sephadex G-10 columns at 298.2 K and are quantitatively analyzed on the basis of stepwise aggregation models. The micellar aggregation numbers, critical micelle concentrations (cmc's), stepwise aggregation constants, and micelle size distributions of TCDC and TUDC are determined and compared to those of sodium taurocholate and taurodeoxycholate. The logarithms of gel−water partition coefficients, dimerization constants, and reciprocal cmc values for the four bile salts exhibit linearity with their hydrophobic molecular surface areas, and the slopes are close to that of the logarithms of reciprocal cmc values against the hydrophobic molecular surface areas of lecithins. This fact shows that the gel adsorption, dimerization, and micellization of bile salts are driven mainly by hydrophobic interactions and that the Small model ...

Tauroursodeoxycholate ameliorates reperfusion injury after pig liver transplantation.

Reperfusion injury is a serious problem after clinical liver transplantation, often leading to dys- or even non-function of grafts. The present study was designed to determine whether the hydrophilic bile salt tauroursodeoxycholate (TUDC), known to be hepatoprotective in cholestatic liver disease, mitigates reperfusion injury in an in vivo pig liver transplantation model. Liver transplantation was performed in 12 pigs after a preservation time of 8 h. TUDC was administered to donor and recipient animals, and saline to controls. Blood was drawn at different time points for determination of liver enzymes. Bile samples were collected, and bile flow (BF), and bile salt secretion rate (BSSR) determined. Samples of liver tissue and bile ducts were taken for assessment by light and electron microscopy. Liver enzymes were significantly lower in the TUDC group. BF and BSSR were significantly higher. Microscopy revealed better preservation of bile duct architecture of the TUDC-infused animals. We can conclude that infusions of TUDC in pig livers ameliorate reperfusion injury in vivo. The molecular basis for this finding may be the membrane stabilizing effect of TUDC. Further studies are warranted to clarify its effect.

Tauroursodeoxycholate ameliorates reperfusion injury after pig liver transplantation

Reperfusion injury is a serious problem after clinical liver transplantation, often leading to dys- or even non-function of grafts. The present study was designed to determine whether the hydrophilic bile salt tauroursodeoxycholate (TUDC), known to be hepatoprotective in cholestatic liver disease, mitigates reperfusion injury in an in vivo pig liver transplantation model. Liver transplantation was performed in 12 pigs after a preservation time of 8 h. TUDC was administered to donor and recipient animals, and saline to controls. Blood was drawn at different time points for determination of liver enzymes. Bile samples were collected, and bile flow (BF), and bile salt secretion rate (BSSR) determined. Samples of liver tissue and bile ducts were taken for assessment by light and electron microscopy. Liver enzymes were significantly lower in the TUDC group. BF and BSSR were significantly higher. Microscopy revealed better preservation of bile duct architecture of the TUDC-infused animals. We can conclude that infusions of TUDC in pig livers ameliorate reperfusion injury in vivo. The molecular basis for this finding may be the membrane stabilizing effect of TUDC. Further studies are warranted to clarify its effect.

In vivo protection of the pig liver against ischemia/reperfusion injury by tauroursodeoxycholate.

Tauroursodeoxycholate (TUDC) is used routinely in the treatment of cholestatic liver disease. The present study was designed to determine whether it would mitigate ischemia/reperfusion injury in an in vivo pig liver-transplantation model. Transplantation was performed in 12 animals after a preservation time of 8 h. In the control group (n=6), 0.9% saline was infused into the donor. In the experimental group (n=6), TUDC was given intravenously at a rate of 2 micromol/kg body weight per minute. In the recipient, infusion was started at the time of reperfusion; saline was infused for 400 min in the control group, TUDC for the same duration at a rate of 0.2 micromol/kg body weight per minute in the experimental group. Blood was drawn for determination of liver enzymes. Bile samples were collected and bile flow (BF) and bile salt secretion rate (BSSR) were determined. One-week survival was 92% and not different among groups. Liver enzymes were lower in the TUDC group than the saline group. Prior to TUDC infusion in the donor animals, there were no differences in BF and BSSR. After infusion of TUDC, BF and BSSR were highly significantly different than the control group. Infusion of TUDC in pig livers protects against ischemia/reperfusion injury in vivo. This might be due to the membrane-stabilizing effect of TUDC. Preconditioning of liver grafts with TUDC could potentially lead to improved liver function post-transplantation.

Tauroursodeoxycholate and S-adenosyl-L-methionine exert an additive ameliorating effect on taurolithocholate-induced cholestasis: a study in isolated rat hepatocyte couplets.

The monohydroxy bile acid, taurolithocholate (TLC), causes cholestasis in vivo and in isolated perfused livers. It is also cholestatic in vitro and, in this study using isolated rat hepatocyte couplets, causes a reduction of the accumulation of (fluorescent) bile acid in the canalicular vacuoles (cVA) of this polarized cell preparation. The hepatoprotective bile acid, tauroursodeoxycholate (TUDCA), partially protects against the action of TLC when added at the same time. It also partially reverses the cholestatic effect if added after the cells have been exposed to TLC. A second hepatoprotective compound, S-adenosyl-L-methionine (SAMe) also not only partially protects against the action of TLC when added at the same time, but it too is able to partially reverse the cholestatic effect. Neither hepatoprotective agent is fully effective alone, but their effects are additive. In combination, a full restoration of cVA is observed in moderate cholestasis, but not in severe cholestasis. We discuss briefly some possible mechanisms involved in the additive mode of action of both hepatoprotective compounds. In summary, we show for the first time that SAMe and TUDCA can exert an additive effect in the amelioration of TLC-induced cholestasis in isolated rat hepatocyte couplets. This finding may be of possible clinical relevance.

Tauroursodeoxycholate and taurochenodeoxycholate stabilize bile lipid metastability through different mechanisms: relation to phospholipid fatty acid composition

Lecithin–cholesterol vesicles are present in bile and play a role in cholesterol metastability. Cholesterol holding capacity of vesicles is regulated by lecithin hydrophobicity. In the present study, the effect of therapeutic bile salts on biliary lipid secretion rate and phospholipid fatty acid composition was evaluated in bile duct-fistula rats to determine whether bile salts modulate biliary phospholipid species to, thereby, regulate a physico-chemical metastability of bile cholesterol. Rats were depleted with bile salt pool by overnight biliary diversion and reinfused intravenously with sodium taurocholate (TC) at a constant rate (200 nmol/min per 100 g b.w.) for 3 h, followed by infusion of either sodium taurochenodeoxycholate (TCDC) or tauroursodeoxycholate (TUDC) at a compatible rate. TCDC-infusion increased the biliary secretion rate of cholesterol and phospholipids with a decrease in molar ratio of cholesterol to phospholipid ( C/ P) when compared to values under TC-infusion, and this was associated with an increase in the molar ratio of phospholipid saturated to unsaturated fatty acids ( S/ U). In contrast, TUDC-infusion decreased such a biliary lipid secretion rate with an increase in C/ P, and this was associated with a decrease in a molar ratio of arachidonate in phospholipids. These findings indicate that TCDC enhances a cholesterol packing density of biliary particulate species by decreasing C/ P ratio and increasing S/ U, whereas TUDC improves bile lithogenecity by decreasing biliary cholesterol and phospholipid secretion rates and reducing bile arachidonyl phospholipids.

Activation of protein kinase C alpha and delta by bile acids: correlation with bile acid structure and diacylglycerol formation

The feedback repression of cholesterol 7alpha-hydroxylase transcriptional activity and mRNA levels by taurocholate (TCA) occurs via a protein kinase C (PKC)-dependent signal. To determine whether bile acids could activate PKC indirectly via generation of diacylglycerol (DG), their effects on DG levels in primary cultures of rat hepatocytes were determined using a DG kinase assay. To determine whether bile acids might activate PKC isozymes more directly, their effects on PKC alpha and delta purified from baculovirus expression systems were examined in phosphatidylserine/phosphatidylcholine/Triton X-100 (PS/PC/TX) mixed micelles. Addition of tauroursodeoxycholate (TUDCA), taurocholate (TCA), or taurodeoxycholate (TDCA) (50 microM) to the cells rapidly (15 min) increased DG content in cultured rat hepatocytes to 105%, 155%, and 130%, respectively, as compared to untreated control cultures. Addition of TCA increased PKC alpha specific activity with EC50 of approximately 400 nM; maximal activity was observed with 5 microM. Other taurine-conjugated bile acids (5 microM) increased PKC alpha specific activity (pmol/min/microg protein) in proportion to their relative hydrophobicity: PS/PC/TX 17 +/- 2; + TUDCA 29 +/- 18; + TCA 68 +/-13; + TDCA 166 +/- 21; and, taurochenodeoxycholate 178 +/- 20 (P vs. PS/PC/TX = 0.54, 0.019, 0.002, and 0.001, respectively); unconjugated bile acids gave similar results (r2 for activity vs. hydrophobicity index 0.59). Taurine-conjugated bile acid interaction enthalpies, as determined by dimyristoyl-phosphatidylcholine chromatography, were more highly correlated (r2 = 0.96) with PKC alpha activation than with the hydrophobicity index. TCA also stimulated the activity of purified PKCdelta with EC50 of approximately 150 nM and maximally (2.7-fold) at 1 microM. Free and taurine-conjugated bile acids (1 microM) increased PKCdelta activity according to their hydrophobicity index (r2 = 0.89) and interaction enthalpies (r2 = 0.96).

Mitogen-activated protein kinases mediate the stimulation of bile acid secretion by tauroursodeoxycholate in rat liver

BACKGROUND & AIMS: Tauroursodeoxycholate (TUDCA) is widely used in the treatment of cholestatic liver disease. The purpose of this study was to elucidate molecular mechanisms underlying its beneficial effect.METHODS: TUDCA-induced signaling towards bile acid excretion was studied in 24-hour-cultured rat hepatocytes and perfused rat liver.RESULTS: In rat hepatocytes, TUDCA (> 100 mumol/L) led within 10 minutes to an activation of the mitogen-activated protein (MAP)-kinases extracellular signal-regulated kinase (Erk)-1 and Erk-2. Erk activation by TUDCA was insensitive to inhibition of protein kinase C, tyrosine kinases, and G-protein function. TUDCA-induced Erk activation, however, was abolished in the presence of PD098059, a MAP-kinase kinase (MAP- kinase/Erk-kinase [MEK]) inhibitor and after elevation of intracellular adenosine 3',5'-cyclic monophosphate. Thus, TUDCA signaling towards MAP kinases is different from hypo-osmotic MAP-kinase activation, which is sensitive to inhibitors of tyrosine kinases and G-protein function. Addition of dibutyryl-adenosine 3',5'-cyclic monophosphate or PD098059 also abolished the stimulatory effect of TUDCA (20 mumol/L) on taurocholate excretion in perfused rat liver, whereas tyrosine kinase inhibition was ineffective.CONCLUSIONS: TUDCA signaling towards bile acid secretion is mediated by an Raf/MEK-dependent activation of MAP kinases. Although both TUDCA and hypo-osmotic hepatocyte swelling lead to MAP-kinase activation and a stimulation of bile acid secretion, different upstream signaling events are involved.(Gastroenterology 1997 Oct;113(4):1306-14)

Cholesterol Binding to Simple Micelles in Aqueous Bile-Salt–Cholesterol Solutions

The true thermodynamic activity (AT) of cholesterol (Ch) in aqueous solutions containing taurocholate (TC)–Ch was determined by employing a direct assay of a 1 × 2-cm silicone polymer film with 0.025 cm thickness. Using theATdata, information on the nature of micellar species present in the TC–Ch system, and employing a binding-site model previously developed for tauroursodeoxycholate (TUDC)–Ch and taurochenodeoxycholate (TCDC)–Ch systems, it appeared that the Ch-binding affinity for simple bile-salt micelles corresponds precisely with the order of hydrophobicity, TUDC < TC < TCDC. Further, although simple TC micelles and simple TCDC micelles have similar binding capacities, the first Ch binding to a simple TC micelle may not significantly facilitate the second Ch binding, as occurs in simple TCDC micelles. For TUDC–Ch, TC–Ch, and TCDC–Ch systems, the concentration of bound simple micelles increased with increasingATvalues, whereas the unbound simple micelle concentration decreased proportionally. These results provide insights into the possible influence of bile-salt species on Ch-binding to simple micelles in bile-salt–Ch solutions.

Membrane cholesterol content of cholesterol/phospholipid vesicles determines the susceptibility to both damage and protection by bile salts: implications for bile physiology.

To investigate the effect of membrane lipid composition on the susceptibility to bile salt damage and protection. Artificial model cholesterol/phospholipid (c/p) membranes (vesicles) with a varying cholesterol (0-15 mM) and phospholipid content (3-30 mM), and with a c/p ratio ranging up to 1.70, were prepared by sonication. We examined the effect of incubation with increasing concentrations of either tauroursodeoxycholate (TUDC), taurocholate (TC) or taurodeoxycholate (TDC) alone, or with proportionally varying mixtures of TUDC and TDC. Vesicle integrity was assessed by the change in optical absorbance at 340 nm. Absorption of the bile salt-vesicle mixture decreased, with increasing bile salt concentration and hydrophobicity: TUDC less than TC less than TDC. Moreover, bile salt-induced damage also depended on membrane composition: vesicles containing more than 5 mM cholesterol and with a c/p ratio greater than 0.8 were less likely to be solubilized by 30 mM bile salt. Similarly, only in cholesterol-rich vesicles (c/p > 0.5) was a protective effect of TUDC against membrane disruption by TDC revealed upon incubation with various TUDC/TDC mixtures. Apart from the bile salt concentration and hydrophobicity, the cholesterol content of vesicles is pivotal, both in the bile salt-induced solubilization of cholesterol/phospholipid vesicles and in the potency of TUDC to prevent this.

Structural mechanisms of bile salt-induced growth of small unilamellar cholesterol-lecithin vesicles.

The liver secretes cholesterol and lecithin in the form of mixed vesicles during the formation of bile. When exposed to bile salts, these metastable vesicles undergo various structural rearrangements. We have examined the effects of three different bile salts, taurocholate (TC), tauroursodeoxycholate (TUDC), and taurodeoxycholate (TDC), on the stability of sonicated lecithin vesicles containing various amounts of cholesterol. Vesicle growth was probed by turbidity measurements, quasi-elastic light scattering, and a resonance energy transfer lipid-mixing assay. Leakage of internal contents was monitored by encapsulation of fluorescence probes in vesicles. At low bile salt-to-lecithin ratios (TC/L or TUDC/L < 1), pure lecithin vesicles do not grow, but exhibit slow intervesicular mixing of lipids as well as gradual leakage. At high BS/L (TC/L or TUDC/L > 5), pure lecithin vesicles are solubilized into mixed micelles with a concomitant decrease in the overall particle size. In this regime, extensive leakage and lipid mixing occur instantaneously after exposure to bile salt. At intermediate BS/L (1 < TC/L or TUDC/L < 5), vesicles grow with time, and the rates of both leakage and lipid mixing are rapid. The data suggest that vesicles grow by the transfer of lecithin and cholesterol via diffusion in the aqueous medium. The addition of cholesterol to lecithin vesicles reduces leakage dramatically and increases the amount of BS required for complete solubilization of vesicles. The more hydrophobic TDC induces vesicle growth at a lower BS/L than does TC or TUDC. These results demonstrate the physiologic forms of lipid microstructures during bile formation and explain how the hydrophilic-hydrophobic balance of BS mixtures may profoundly affect the early stages of CH gallstone formation.

Inhibitory effect of bile salts on gallbladder smooth muscle contractility in the guinea pig in vitro

BACKGROUND & AIMS: Impaired gallbladder emptying occurs in patients undergoing bile salt therapy for cholesterol gallstone dissolution and in patients with cirrhosis who have elevated serum bile salt concentrations. To determine if bile salts directly inhibit gallbladder contractility, isometric contraction of the guinea pig gallbladder was examined in vitro. METHODS: Contractile responses to cholecystokinin (CCK), bethanechol, KCI, and field stimulation were constructed alone and in the presence of selected bile salts: taurodeoxycholate (TDC), taurochenodeoxycholate, taurocholate, and tauroursodeoxycholate (TUDC). RESULTS: More hydrophobic bile salts, such as TDC (as low as 5 micromol/L), concentration-dependently depressed (P < 0.05) both CCK- and field stimulation-induced gallbladder contractions. More hydrophilic bile salts, such as TUDC, only caused a modest depression up to a concentration of 500 micromol/L. When 5 or 50 micromol/L of TUDC was added to the organ bath before the application of equalmolar TDC, the TDC-induced impaired gallbladder contractility was reversed. Thus, this inhibitory effect on gallbladder contraction depended on the hydrophobicity of bile salts and was also specific for certain stimuli such as CCK and field stimulation (mediated by cholinergic nerves, being abolished by atropine and tetrodotoxin). CONCLUSIONS: Such direct bile salt inhibition of CCK- and cholinergic nerve-induced gallbladder contraction may contribute to the deteriorating gallbladder emptying in patients undergoing bile salt therapy for stone dissolution and in cirrhotic patients who are at risk for gallstone formation. (Gastroenterology 1997 May;112(5):1699-706)

Improvement of Estradiol- 17β-D-Glucuronide-Induced Cholestasis by Sodium Tauroursodeoxycholate Therapy in Rats

Background: Estradiol-17β-D-glucuronide (E-17G), a metabolite of natural estrogen, is well known to cause intrahepatic cholestasis in humans. We therefore investigated the effect of sodium tauroursodeoxycholate (T-UDCA), on E-17G-induced cholestasis in female rats. Methods: For die evaluation of the drug, animals given E-17G (10 µmol/kg) were divided into three groups, and T-UDCA was administered intravenously at various doses after E-17G treatment. Results: T-UDCA significantly prevented a marked reduction of bile flow in E-17G-treated rats in all experimental schedules. Furthermore, T-UDCA significantly increased the biliary E-17G excretion rate at an early stage after E-17G treatment in rats. However, this drug caused no significant change in the biliary excretion rate of estradiol-3-sulfate-17β-D-glucuronide (E-3S-17G), which is identified as the major biliary metabolite with E-17G throughout me recovery periods. Conclusion: These results suggest that T-UDCA can improve E-17G-induced acute cholestasis by rapidly increasing the biliary E-17G excretion rate. Thus our finding may provide a useful approach for attempts to prevent drug-induced acute cholestasis in humans.

Mechanism of bile salt-induced mucin secretion by cultured dog gallbladder epithelial cells

1. Hypersecretion of gallbladder mucin has been proposed to be a pathogenic factor in cholesterol gallstone formation. Using cultured gallbladder epithelial cells, we demonstrated that bile salts regulate mucin secretion by the gallbladder epithelium. In the present study we have investigated whether established second messenger pathways are involved in bile salt-induced mucin secretion. 2. The effect of activators and inhibitors on mucin secretion was studied by measuring the secretion of [3H]N-acetyl-D-glucosamine-labelled glycoproteins. Intracellular cAMP content of the cells was measured using a radioimmunoassay. 3. Incubation of the cells with 10 mM taurocholate did not increase the intracellular cAMP content (25.7 versus control 22.8 pmol of cAMP/mg of protein). No stimulation of mucin secretion was observed after incubation with 1-100 microM concentrations of the calcium ionophores ionomycin and A23187. The stimulatory effect of 10 mM tauroursodeoxycholate (TUDC) on mucin secretion could not be inhibited by the addition of EDTA. Activation of protein kinase C (PKC) by 1 microgram/ml phorbol 12-myristate 13-acetate (PMA) caused an increase in mucin secretion (342% versus control 100%), comparable with the effect of 40 mM TUDC. The effect of 10 ng/ml PMA could partially be inhibited by a concentration of 2 microM of the PKC inhibitor staurosporin. Staurosporin had no inhibitory effect on mucin secretion induced by TUDC. 4. In gallbladder epithelial cells bile salts do not stimulate mucin secretion via one of the classical signal transduction pathways. We hypothesize that bile salts act on mucin secretion via a direct interaction with the apical membrane.

Uncoupling of biliary phospholipid and cholesterol secretion in mice with reduced expression of mdr2 P-glycoprotein

Mice in which the gene for mdr2 P-glycoprotein has been disrupted have a severe deficiency in biliary phospholipid and cholesterol secretion. We studied the relation between mdr2 gene expression and biliary lipid secretion with emphasis on the role of bile salt hydrophobicity. Control mice (+/+), and mice with a homozygous (-/-) or heterozygous (+/-) disruption of the mdr2 gene, were infused with taurodeoxycholate (TDC) or tauroursodeoxycholate (TUDC). In mdr2 (-/-) mice, virtually no phospholipids were secreted into bile, irrespective of the type of bile salt infused. In contrast, cholesterol secretion in (-/-) mice increased upon TDC infusion from less than 0.1 to more than 2 nmol/min . 100 g, which was similar to controls under the same conditions. After infusion of TUDC in (-/-) mice. cholesterol secretion also rose (to 1.8 nmol/min . 100 g) but remained much lower than in controls (8 nmol/min x 100 g). In (+/-) mice, cholesterol secretion was equal to (+/+) mice during secretion of endogenous bile salts and during TDC infusion, but was 50% of control levels during maximal TUDC infusion. We conclude that biliary phospholipid secretion completely depends on mdr2 gene expression but cholesterol can, at least partially, be secreted in an mdr2 Pgp-independent mechanism. The extent to which cholesterol is secreted via this mechanism may depend on the hydrophobicity (i.e., cholesterol-solubilizing capacity) of the secreted bile salt.

Modulation of rat hepatocyte proliferation by bile salts: In vitro and In vivo studies

In this study, the stimulatory effect of bile salts (BS) was evaluated both In vitro, using hepatocyte primary cultures, and In vivo, in normal and 40% partially hepatectomized rats previously fed on BS- enriched diets for 4 weeks. In vitro results show that conjugated cholate (CA) and chenodeoxycholate (CDCA) augmented proliferative activity in rat hepatocytes cultured in absence of mitogens, whereas conjugated deoxycholate (DCA), and ursodeoxycholate (UDCA) did not have any significant effect. None of these BSs increased significantly the replicative response induced by submaximal concentrations of epidermal growth factor (EGF). In vivo, at the end of dietary treatment all animals fed on CA or DCA but not those fed on either CDCA, or UDCA, or tauroursodeoxycholate (TUDCA) developed cholestatic hepatitis and a burst of damage-induced hepatocyte proliferation. After 40% partial hepatectomy (PH), CA- and DCA-treated groups underwent a deterioration of cholestatic hepatitis. On the other hand, in CDCA-, and UDCA-, and TUDCA-treated groups liver histology, serum glutamic pyruvic transaminase (SGPT) and cholestasis indices did not change significantly compared with controls. As far as the proliferative activity, a significant increase was observed not only in CA and DCA but also in UDCA- and TUDCA-fed groups compared with controls, whereas a slight decrease was observed in CDCA-treated animals. In conclusion, our data indicate that conjugated BSs had only a modest stimulatory effect on hepatocyte proliferation In vitro. However, In vivo, in PH rats, UDCA or TUDCA treatment determined a further increase of hepatocellular proliferation not attributable to hepatotoxic effects. Our result suggest that modifications of bile acid pool could modulate hepatocellular proliferation.

Modulation of rat hepatocyte proliferation by bile salts: In vitro and In vivo studies

In this study, the stimulatory effect of bile salts (BS) was evaluated both In vitro, using hepatocyte primary cultures, and In vivo, in normal and 40% partially hepatectomized rats previously fed on BS- enriched diets for 4 weeks. In vitro results show that conjugated cholate (CA) and chenodeoxycholate (CDCA) augmented proliferative activity in rat hepatocytes cultured in absence of mitogens, whereas conjugated deoxycholate (DCA), and ursodeoxycholate (UDCA) did not have any significant effect. None of these BSs increased significantly the replicative response induced by submaximal concentrations of epidermal growth factor (EGF). In vivo, at the end of dietary treatment all animals fed on CA or DCA but not those fed on either CDCA, or UDCA, or tauroursodeoxycholate (TUDCA) developed cholestatic hepatitis and a burst of damage-induced hepatocyte proliferation. After 40% partial hepatectomy (PH), CA- and DCA-treated groups underwent a deterioration of cholestatic hepatitis. On the other hand, in CDCA-, and UDCA-, and TUDCA-treated groups liver histology, serum glutamic pyruvic transaminase (SGPT) and cholestasis indices did not change significantly compared with controls. As far as the proliferative activity, a significant increase was observed not only in CA and DCA but also in UDCA- and TUDCA-fed groups compared with controls, whereas a slight decrease was observed in CDCA-treated animals. In conclusion, our data indicate that conjugated BSs had only a modest stimulatory effect on hepatocyte proliferation In vitro. However, In vivo, in PH rats, UDCA or TUDCA treatment determined a further increase of hepatocellular proliferation not attributable to hepatotoxic effects. Our result suggest that modifications of bile acid pool could modulate hepatocellular proliferation. (Hepatology 1996 May;23(5):1159-66)

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.