Taurocholate induces changes in rat cardiomyocyte contraction and calcium dynamics. (33/278)

Obstetric cholestasis is characterized by raised bile acids, and can be complicated by intrauterine death. We have shown that the bile acid taurocholate causes loss of synchronous beating, bradycardia and cessation of contraction in cultured rat cardiomyocytes [Williamson, Gorelik, Eaton, Lab, de Swiet and Korchev (2001) Clin. Sci. 100, 363-369]. The aim of the present study was to investigate the effect of taurocholate on cardiomyocytes further. We demonstrated a reduced rate of contraction and proportion of beating cells when rat cardiomyocytes were exposed to increasing concentrations of taurocholate (0.1-3.0 mM); more marked at higher concentrations (P<0.001). Using scanning ion-conductance microscopy, we also demonstrated reduced amplitude of contraction and calcium transients with taurocholate. Our observations indicate that taurocholate affects calcium release from the sarcoplasmic reticulum and this parallels changes in contractile function. The relationship between the contraction amplitude and calcium transient is not linear, particularly at higher concentrations of taurocholate. We observed different effects in individual cultured neonatal cells; a reversible reduction in rate and amplitude of contraction in some, and irreversible oscillatory (fibrillatory) cessation of beating in others. The effects were more marked with higher concentrations. The contraction amplitude was also reduced in adult cardiomyocytes. The changes were reversible following removal of taurocholate in adult, but not in neonatal, cardiomyocytes exposed to higher concentrations (>0.3 mM) (P<0.001). In conclusion we have demonstrated that the bile acid taurocholate can cause different types of dysrhythmia in individual cardiomyocytes. These results provide further support for the hypothesis that obstetric cholestasis may produce cardiac-related sudden intrauterine death.  (+info)

Effects of bile acids on dog pancreatic duct epithelial cell secretion and monolayer resistance. (34/278)

Pancreatic duct epithelial cells (PDEC) mediate the secretion of fluid and electrolytes and are exposed to refluxed bile. In nontransformed cultured dog PDEC, which express many ion transport pathways of PDEC, 1 mM taurodeoxycholic acid (TDCA) stimulated an (125)I(-) efflux inhibited by DIDS and 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) and a (86)Rb(+) efflux inhibited by charybdotoxin. Inhibition by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-AM suggests mediation via increased intracellular Ca(2+) concentration, whereas the absence of lactate dehydrogenase release excludes cellular toxicity. At 1 mM, TDCA stimulated a larger (125)I(-) efflux than glycodeoxycholate; two dihydroxy bile acids, taurochenodeoxycholate and TDCA, were similarly effective, whereas a trihydroxy bile acid, taurocholate, was ineffective. In Ussing chambers, 1 mM serosal or 2 mM luminal TDCA stimulated an I(sc) increase from confluent PDEC monolayers. TDCA also stimulated 1) a short-circuit current (I(sc)) increase from basolaterally permeabilized PDEC subject to a serosal-to-luminal Cl(-) gradient that was inhibited by BAPTA-AM, DIDS, and NPPB and 2) an I(sc) increase from apically permeabilized PDEC subject to a luminal-to-serosal K(+) gradient inhibited by BAPTA-AM and charybdotoxin. Along with the efflux studies, these findings suggest that TDCA interacts directly with PDEC to stimulate Ca(2+)-activated apical Cl(-) channels and basolateral K(+) channels. Monolayer transepithelial resistance was only minimally affected by 1 mM serosal and 2 mM luminal TDCA but decreased after exposure to higher TDCA concentrations (2 mM serosal and 4 mM luminal). A secretory role for bile acids should be considered in pancreatic diseases associated with bile reflux.  (+info)

Taurocholate feeding prevents CCl4-induced damage of large cholangiocytes through PI3-kinase-dependent mechanism. (35/278)

Bile acids are cytoprotective in hepatocytes by activating phosphatidylinositol-3-kinase (PI3-K) and its downstream signal AKT. Our aim was to determine whether feeding taurocholate to CCl(4)-treated rats reduces cholangiocyte apoptosis and whether this cytoprotective effect is dependent on PI3-K. Cholangiocyte proliferation, secretion, and apoptosis were determined in cholangiocytes from bile duct ligation (BDL), CCl(4)-treated BDL rats, and CCl(4)-treated taurocholate-fed rats. In vitro, we tested whether CCl(4) induces apoptosis and whether loss of cholangiocyte proliferation and secretion is dependent on PI3-K. The CCl(4)-induced cholangiocyte apoptosis and loss of cholangiocyte proliferation and secretion were reduced in CCl(4)-treated rats fed taurocholate. CCl(4)-induced cholangiocyte apoptosis, loss of cholangiocytes secretion, and proliferation were prevented by preincubation with taurocholate. Taurocholate cytoprotective effects were ablated by wortmannin. Taurocholate prevented, in vitro, CCl(4)-induced decrease of phosphorylated AKT protein expression in cholangiocytes. The cytoprotective effects of taurocholate on CCl(4) effects on cholangiocyte proliferation and secretion were abolished by wortmannin. Taurocholate protects cholangiocytes from CCl(4)-induced apoptosis by a PI3-K-dependent mechanism. Bile acids are important in the prevention of drug-induced ductopenia in cholangiopathies.  (+info)

Improvement of alanine aminotransferase by administration of suplatast tosilate plus ursodeoxycholic acid in patients with resistance to ursodeoxycholic acid monotherapy on hepatitis C virus-related chronic liver disease. (36/278)

OBJECTIVE: Inflammatory liver damage and viral persistence after hepatitis C virus (HCV) infection are known to be related in host immunity. Suplatast tosilate is an immunomodulator that selectively inhibits type 2 cytokine production by helper T cells. We investigated the efficacy and safety of the administration of suplatast tosilate for patients with HCV infection by examining the level of serum alanine aminotransferase (ALT) and viremia. PATIENTS AND METHODS: Thirty-eight patients who had shown resistance to ursodeoxycholic acid (UDCA) therapy (600 mg/day tid) over 6 months for HCV-related chronic liver disease were randomized into two groups and received UDCA alone (600 mg/day tid) or UDCA (600 mg/day tid) plus suplatast tosilate (300 mg/day tid) by means of sealed envelopes. RESULTS: After 24 weeks, serum ALT was decreased in the patients receiving UDCA plus suplatast tosilate, with the mean reduction being 40.2% (from 132 to 79 IU/l; p=0.001). In the patients receiving UDCA alone, ALT decreased by 8.3% (from 133 to 122 IU/l; ns). Multiple comparison of individual ALT changes showed that the UDCA plus suplatast tosilate achieved significantly greater improvement (p = 0.001). However, serum HCV RNA was unchanged in both groups. Two patients developed adverse reactions to suplatast tosilate, which resolved promptly after the discontinuation of the therapy. CONCLUSION: These findings suggest that suplatast tosilate promotes biochemical improvement in the patients with chronic hepatitis C.  (+info)

Ursodeoxycholic acid inhibits the initiation and postinitiation phases of azoxymethane-induced colonic tumor development. (37/278)

Colonic tumorigenesis involves the processes of initiation and promotion/progression from normal epithelial cells to tumors. Studies in both humans and experimental models of colon cancer indicate that secondary bile acids promote tumor development. In contrast, we have demonstrated previously that another bile acid, ursodeoxycholic acid (UDCA), inhibits the development of azoxymethane (AOM)-induced colon cancer in rats. More recently, we have shown that UDCA inhibits AOM-induced hyperproliferation, and aberrant crypt formation and growth. In our previous studies, we supplemented UDCA throughout the experiment. The efficacy of a chemopreventive agent may depend on the timing of administration, which has important clinical implications. In the present investigation, we examined the ability of UDCA, when administered only in the initiation or the promotion/progression phase, to block tumor development. Male Fisher 344 rats were divided in a 2 x 3 factorial design, with animals receiving AOM or vehicle, and fed an unsupplemented diet or diet supplemented with 0.4% UDCA in the initiation or promotion/progression phase. Thirty-two weeks later, rats were sacrificed and tumor histology determined, and colons were examined for aberrant crypt foci (ACF). In the carcinogen-treated dietary control group, tumor incidence was 72.3%, and tumor multiplicity was 1.9 tumors per tumor-bearing rat. UDCA, in the initiation or promotion/progression phase, significantly decreased tumor incidence to 46.2% and 38.4% (P < 0.05), respectively; and tumor multiplicity to 1.4 and 1.3 tumors per tumor-bearing rat (P < 0.05), respectively. UDCA did not alter tumor size, histology, or location, although there were trends for smaller tumors and less advanced histological grades in the group given UDCA during the promotion phase. UDCA, in the initiation but not the promotion phase, inhibited ACF formation and growth. In summary, UDCA significantly inhibited AOM-induced colonic carcinogenesis during either tumor initiation or in the promotion/progression phase. In contrast, UDCA inhibited ACF formation only when administered in the initiation phase, suggesting that the mechanisms of chemoprevention by this bile acid differ in these two phases.  (+info)

Taurolithocholic acid exerts cholestatic effects via phosphatidylinositol 3-kinase-dependent mechanisms in perfused rat livers and rat hepatocyte couplets. (38/278)

Taurolithocholic acid (TLCA) is a potent cholestatic agent. Our recent work suggested that TLCA impairs hepatobiliary exocytosis, insertion of transport proteins into apical hepatocyte membranes, and bile flow by protein kinase Cepsilon (PKCepsilon)-dependent mechanisms. Products of phosphatidylinositol 3-kinases (PI3K) stimulate PKCepsilon. We studied the role of PI3K for TLCA-induced cholestasis in isolated perfused rat liver (IPRL) and isolated rat hepatocyte couplets (IRHC). In IPRL, TLCA (10 micromol/liter) impaired bile flow by 51%, biliary secretion of horseradish peroxidase, a marker of vesicular exocytosis, by 46%, and the Mrp2 substrate, 2,4-dinitrophenyl-S-glutathione, by 95% and stimulated PI3K-dependent protein kinase B, a marker of PI3K activity, by 154% and PKCepsilon membrane binding by 23%. In IRHC, TLCA (2.5 micromol/liter) impaired canalicular secretion of the fluorescent bile acid, cholylglycylamido fluorescein, by 50%. The selective PI3K inhibitor, wortmannin (100 nmol/liter), and the anticholestatic bile acid tauroursodeoxycholic acid (TUDCA, 25 micromol/liter) independently and additively reversed the effects of TLCA on bile flow, exocytosis, organic anion secretion, PI3K-dependent protein kinase B activity, and PKCepsilon membrane binding in IPRL. Wortmannin also reversed impaired bile acid secretion in IRHC. These data strongly suggest that TLCA exerts cholestatic effects by PI3K- and PKCepsilon-dependent mechanisms that are reversed by tauroursodeoxycholic acid in a PI3K-independent way.  (+info)

Transport of taurocholate by mutants of negatively charged amino acids, cysteines, and threonines of the rat liver sodium-dependent taurocholate cotransporting polypeptide Ntcp. (39/278)

The relevance of functional amino acids for taurocholate transport by the sodium-dependent taurocholate cotransporting polypeptide Ntcp was determined by site-directed mutagenesis. cRNA from 28 single-points mutants of the rat liver Ntcp clone was expressed in Xenopus laevis oocytes. Mutations were generated in five conserved negatively charged amino acids (aspartates and glutamates) which were present in nine members of the SBAT-family, in two nonconserved negatively charged amino acids, in all eight Ntcp-cysteines, and in two threonines from a protein kinase C consensus region of the Ntcp C-terminus. Functional amino acids were Asp115, Glu257, and Cys266, which were found to be essential for the maintenance of taurocholic acid transport. Asp115 is located in the large intracellular loop III, whereas Glu257 and Cys266 are located in the large extracellular loop VI. Four mutations of threonines from the C-terminus of the Ntcp by alanines or tyrosines showed no effects on sodium-dependent taurocholate transport. Introduction of the FLAG(R) motif into several transport negative point mutations demonstrated that all mutated proteins besides one were present within the cell membrane of the oocytes and provided proof that an insertion defect has not caused transport deficiency by these Ntcp mutants. The latter was observed only with the transport negative mutant Asp24Asn. In conclusion, loop amino acids are required for sodium-dependent substrate translocation by the Ntcp.  (+info)

Review article: pruritus in cholestatic and other liver diseases. (40/278)

Pruritus is often the most troublesome symptom in patients with chronic liver disease, particularly when cholestasis is a prominent feature. The exact pathogenesis is unknown, but empirical treatment, such as cholestyramine, based on a liver-based origin of pruritus, has been used for many years. Recently, evidence for a central mechanism for pruritus has been obtained and opioid antagonists have been tried clinically with some benefit, but their use is not widespread. In addition, the pruritus associated with intrahepatic cholestasis of pregnancy can now be alleviated in many cases by ursodeoxycholic acid. As it also improves foetal outcome, this should become first-line therapy. We review the pathogenesis and therapy of pruritus, highlighting practical aspects to help with patients with seemingly intractable pruritus.  (+info)