Glycochenodeoxycholate-induced lethal hepatocellular injury in rat hepatocytes. Role of ATP depletion and cytosolic free calcium

Ursodeoxycholate protects against ethanol-induced liver mitochondrial injury

The purpose of this work was to examine whether ursodeoxycholate (UDC), a hydrophilic bile salt, could reduce mitochondrial liver injury from chronic ethanol consumption in rats. Animals were pair-fed liquid diets containing 36% of calories as ethanol or isocaloric carbohydrates. They were randomly assigned into 4 groups of 7 rats each and received a specific treatment for 5 weeks: control diet, ethanol diet, control diet + UDC, and ethanol diet + UDC. Respiratory rates of isolated liver mitochondria were measured using a Clark oxygen electrode with sodium succinate as substrate. Mitochondria from rats chronically fed ethanol demonstrated an impaired ability to produce energy. At the fatty liver stage, the ADP-stimulated respiration (V3) was depressed by 33%, the respiratory control ratio (RC) by 25% and the P/O ratio by 15%. In ethanol-fed rats supplemented with UDC, both the rate and efficiency of ATP synthesis via the oxidative phosphorylation were improved: V3 was increased by 35%, P/O by 8%. All the respiratory parameters were similar in control group and control + UDC group. On the other hand, the number and size of mitochondria were assessed by electron microscopy and computer-assisted quantitative analysis. The number of mitochondria from ethanol-treated rats was decreased by 29%, and they were enlarged by 74%. Both parameters were normalized to control values by UDC treatment. These studies demonstrate that UDC has a protective effect against ethanol-induced mitochondrial injury by improving ATP synthesis and preserving liver mitochondrial morphology. These UDC positive effects may contribute to the observed decrease in fat accumulation and may delay the progression of alcoholic injury to more advanced stages.

Cholestasis confers resistance to the rat liver mitochondrial permeability transition

BACKGROUND & AIMS

Bile salts can cause hepatocyte death by inducing the mitochondrial permeability transition (MPT). However, the slow progression of human cholestatic liver diseases suggests that hepatocytes adapt to resist the MPT. Bcl-x, a protein, and increased mitochondrial cardiolipin, a membrane lipid, elevate the threshold for the MPT. Our aims were to determine if liver mitochondria become resistant to the MPT during cholestasis and, if so, if the resistance is mediated by Bcl-x and/or increased cardiolipin.

METHODS

Hepatocytes and liver mitochondria were obtained from bile duct-ligated (BDL) rats and sham-operated rats (control).

RESULTS

After addition of glycochenodeoxycholate (GCDC), the magnitude of the MPT was reduced in mitochondria from BDL rats vs. controls. Although Bcl-xL was not increased, mitochondrial cardiolipin content was significantly greater in BDL rats vs. controls. Cell viability was also increased in hepatocytes from BDL rats vs. controls after treatment with GCDC. Feeding BDL rats a fatty acid-deficient diet prevented the increase in mitochondrial cardiolipin content; mitochondria and hepatocytes from these rats were susceptible to the MPT and hepatocellular death by GCDC.

CONCLUSIONS

These data suggest that an increase in mitochondria cardiolipin content occurs during cholestasis as an adaptive phenomenon to resist cell death by the MPT.

The effect of idebenone, a coenzyme Q analogue, on hydrophobic bile acid toxicity to isolated rat hepatocytes and hepatic mitochondria

Oxidant stress induced by hydrophobic bile acids has been implicated in the pathogenesis of liver injury in cholestatic liver disorders. We evaluated the effect of idebenone, a coenzyme Q analogue, on taurochenodeoxycholic acid (TCDC)-induced cell injury and oxidant stress in isolated rat hepatocytes and on glycochenodeoxycholic acid (GCDC)-induced generation of hydroperoxides in fresh hepatic mitochondria. Isolated rat hepatocytes in suspension under 9% oxygen atmosphere were preincubated with 0, 50, and 100 micromol/l idebenone for 30 min and then exposed to 1000 micromol/l TCDC for 4 h. LDH release (cell injury) and thiobarbituric acid reactive substances (measure of lipid peroxidation) increased after TCDC exposure but were markedly suppressed by idebenone pretreatment. In a second set of experiments, the addition of 100 micromol/l idebenone up to 3 h after hepatocytes were exposed to 1000 micromol/l TCDC resulted in abrogation of subsequent cell injury and markedly reduced oxidant damage to hepatocytes. Chenodeoxycholic acid concentrations increased to 5.15 nmol/10(6) cells after 2 h and to 7.05 after 4 h of incubation of hepatocytes with 1000 micromol/l TCDC, and did not differ in the presence of idebenone. In freshly isolated rat hepatic mitochondria, when respiration was stimulated by succinate, 10 micromol/l idebenone abrogated the generation of hydroperoxides during a 90-minute exposure to 400 micromol/l GCDC. These data demonstrate that idebenone functions as a potent protective hepatocyte antioxidant during hydrophobic bile acid toxicity, perhaps by reducing generation of oxygen free radicals in mitochondria.

Induction of the mitochondrial permeability transition as a mechanism of liver injury during cholestasis: a potential role for mitochondrial proteases

As part of this thematic series on mitochondria in cell death, we would like to review our data on: (1) the role of the mitochondrial permeability transition (MPT) in hepatocyte necrosis during cholestasis; and (2) the concept that endogenous mitochondrial protease activity may lead to the MPT. Many chronic human liver diseases are characterized by cholestasis, an impairment in bile flow. During cholestasis an accumulation of toxic hydrophobic bile salts in the hepatocyte causes necrosis. We tested the hypothesis that toxic hydrophobic bile salt, glycochenodeoxycholate (GCDC), causes hepatocyte necrosis by inducing the MPT. GCDC induces a rapid, cyclosporin A-sensitive MPT. The hydrophilic bile salt, ursodeoxycholate (UDCA), prevents the GCDC-induced MPT and hepatocyte necrosis providing an explanation for its beneficial effect in human liver disease. We have also demonstrated that the calcium-dependent MPT is associated with an increase in calpain-like protease activity and inhibited by calpain inhibitors. In an experimental model of cholestasis, mitochondrial calpain-like protease activity increases 1.6-fold. We propose for the first time that activation of mitochondrial proteases may initiate the MPT and cell necrosis during cholestasis.

Role of calcium in adaptive cytoprotection and cell injury induced by deoxycholate in human gastric cells

We have developed an in vitro model of adaptive cytoprotection induced by deoxycholate (DC) in human gastric cells and have shown that pretreatment with a low concentration of DC (mild irritant, 50 microM) significantly attenuates injury induced by a damaging concentration of DC (250 microM). This study was undertaken to assess the effect of the mild irritant on changes in intracellular Ca2+ and to determine if these perturbations account for its protective action. Protection conferred by the mild irritant was lost when any of its effects on intracellular Ca2+ were prevented: internal Ca2+ store release via phospholipase C and inositol 1,4, 5-trisphosphate sustained Ca2+ influx through store-operated Ca2+ channels or eventual Ca2+ efflux. We also investigated the relationship between Ca2+ accumulation and cellular injury induced by damaging concentrations of DC. In cells exposed to high concentrations of DC, sustained Ca2+ accumulation as a result of extracellular Ca2+ influx, but not transient changes in intracellular Ca2+ content, appeared to precede and induce cellular injury. We propose that the mild irritant disrupts normal Ca2+ homeostasis and that this perturbation elicits a cellular response (involving active Ca2+ efflux) that subsequently provides a protective action by limiting the magnitude of intracellular Ca2+ accumulation.

Contribution of hepatic parenchymal and nonparenchymal cells to hepatic fibrogenesis in biliary atresia

Extrahepatic biliary atresia is a severe neonatal liver disease resulting from a sclerosing cholangiopathy of unknown etiology. Although biliary obstruction may be surgically corrected by a "Kasai" hepatoportoenterostomy, most patients still develop progressive hepatic fibrosis, although the source of increased collagen deposition is unclear. This study examined the role of hepatic stellate cells (HSCs) and assessed the source of transforming growth factor-beta (TGF-beta) production in hepatic fibrogenesis in patients with biliary atresia. Liver biopsies from 18 biliary atresia patients (including 5 pre- and post-Kasai) were subjected to immunohistochemistry for alpha-smooth muscle actin and in situ hybridization for either procollagen alpha1 (I) mRNA or TGF-beta1 mRNA. Sections were also subjected to immunohistochemistry for active TGF-beta1 protein. The role of Kupffer cells in TGF-beta1 production was assessed by immunohistochemistry for CD68. Procollagen alpha1 (I) mRNA was colocalized to alpha-smooth muscle actin-positive HSCs within the region of increased collagen protein deposition in fibrotic septa and surrounding hyperplastic bile ducts. The number of activated HSCs was decreased in only one post-Kasai biopsy. TGF-beta1 mRNA expression was demonstrated in bile duct epithelial cells and activated HSCs and in hepatocytes in close proximity to fibrotic septa. Active TGF-beta1 protein was demonstrated in bile duct epithelial cells and activated HSCs. This study provides evidence that activated HSCs are responsible for increased collagen production in patients with biliary atresia and therefore play a definitive role in the fibrogenic process. We have also shown that bile duct epithelial cells, HSCs, and hepatocytes are all involved in the production of the profibrogenic cytokine, TGF-beta1.

Effect of S-adenosylmethionine versus tauroursodeoxycholic acid on bile acid-induced apoptosis and cytolysis in rat hepatocytes

BACKGROUND

S-adenosylmethionine (SAMe) increases survival in alcoholic liver cirrhosis and may have a beneficial effect in cholestatic liver disease. SAMe repletes glutathione stores and protects tissue from oxygen free radicals. The effect of SAMe on bile acid-induced apoptosis is unknown. In the present study the possible hepatoprotective effect of SAMe was evaluated and compared with that of tauroursodeoxycholic acid (TUDCA).

METHODS

Primary rat hepatocytes treated with glycochenodeoxycholic acid (GCDCA) were used as a model for cholestasis-induced hepatocellular damage, which served to study the effects of SAMe and TUDCA on bile acid-induced apoptosis and cytolysis.

RESULTS

SAMe reduced bile acid-induced apoptosis but did not prevent bile acid-induced cytolysis. Compared with SAMe, TUDCA was more efficient in reducing apoptosis due to toxic bile acids. The combination of SAMe and TUDCA had additive effects in reducing apoptosis.

CONCLUSION

The reduction in bile acid-induced apoptosis by SAMe may represent one of the factors responsible for its beneficial effects in the treatment of liver diseases.

A novel role for ursodeoxycholic acid in inhibiting apoptosis by modulating mitochondrial membrane perturbation

The hydrophilic bile salt ursodeoxycholic acid (UDCA) protects against the membrane-damaging effects associated with hydrophobic bile acids. This study was undertaken to (a) determine if UDCA inhibits apoptosis from deoxycholic acid (DCA), as well as from ethanol, TGF-beta1, Fas ligand, and okadaic acid; and to (b) determine whether mitochondrial membrane perturbation is modulated by UDCA. DCA induced significant hepatocyte apoptosis in vivo and in isolated hepatocytes determined by terminal transferase-mediated dUTP-digoxigenin nick end-labeling assay and nuclear staining, respectively (P < 0.001). Apoptosis in isolated rat hepatocytes increased 12-fold after incubation with 0.5% ethanol (P < 0.001). HuH-7 cells exhibited increased apoptosis with 1 nM TGF-beta1 (P < 0. 001) or DCA at >/= 100 microM (P < 0.001), as did Hep G2 cells after incubation with anti-Fas antibody (P < 0.001). Finally, incubation with okadaic acid induced significant apoptosis in HuH-7, Saos-2, Cos-7, and HeLa cells. Coadministration of UDCA with each of the apoptosis-inducing agents was associated with a 50-100% inhibition of apoptotic changes (P < 0.001) in all the cell types. Also, UDCA reduced the mitochondrial membrane permeability transition (MPT) in isolated mitochondria associated with both DCA and phenylarsine oxide by > 40 and 50%, respectively (P < 0.001). FACS(R) analysis revealed that the apoptosis-inducing agents decreased the mitochondrial transmembrane potential and increased reactive oxygen species production (P < 0.05). Coadministration of UDCA was associated with significant prevention of mitochondrial membrane alterations in all cell types. The results suggest that UDCA plays a central role in modulating the apoptotic threshold in both hepatocytes and nonliver cells, and inhibition of MPT is at least one pathway by which UDCA protects against apoptosis.

Cyclic adenosine monophosphate-mediated protection against bile acid-induced apoptosis in cultured rat hepatocytes

Cyclic adenosine monophosphate (cAMP) has been shown to modulate apoptosis. To evaluate the role of cAMP in bile acid-induced hepatocyte apoptosis, we studied the effect of agents that increase cAMP on the induction of apoptosis by glycochenodeoxycholate (GCDC) in cultured rat hepatocytes. GCDC induced apoptosis in 26.5%+/-1.1% of hepatocytes within 2 hours. Twenty-minute pretreatment of hepatocytes with 100 micromol/L 8-(4-chlorothiophenyl) cAMP (CP-cAMP) resulted in a reduction in the amount of apoptosis to 35.2%+/-3.8% of that seen in hepatocytes treated with GCDC alone. Other agents that increase intracellular cAMP, including dibutyryl cAMP (100 micromol/L), glucagon (200 nmol/L), and a combination of forskolin (20 micromol/L) and 3-isobutyl-1-methylxanthine (20 micromol/L), also inhibited GCDC-induced apoptosis to a similar extent. Pretreatment with the protein kinase A (PKA) inhibitor, KT5720, prevented the protective effect of CP-cAMP and inhibited CP-cAMP-induced activation of PKA activity. Inhibitors of phosphatidylinositol 3-kinase (PI3K), wortmannin (50 nmol/L), or Ly 294002 (20 micromol/L) also prevented the cytoprotective effect of cAMP. PI3K assays confirmed that wortmannin (50 nmol/L) inhibited PI3K activity, while CP-cAMP had no effect on the activity of this lipid kinase. GCDC increased mitogen-activated protein kinase (MAPK) activity, but had no effect on stress-activated protein kinase (SAPK) activity in hepatocytes. cAMP decreased basal and GCDC-induced MAPK activity and increased SAPK activity. The MAPK kinase inhibitor, PD 98059, inhibited both GCDC-mediated MAPK activation and GCDC-induced apoptosis.

IN CONCLUSION

1) agents that increase intracellular cAMP protect against hepatocyte apoptosis induced by hydrophobic bile acids; 2) activation of MAPK by GCDC may be involved in bile acid-induced apoptosis; and 3) cAMP-mediated cytoprotection against bile acid-induced apoptosis appears to involve PKA, MAPK, and PI3K.

Effect of high concentrations of bile acids on cultured hepatocytes

High concentrations of bile acids have been reported as injurious to hepatocytes. We report the influence of various combinations of bile acids on the liver-specific function of cultured rat hepatocytes. Using 4 bile acids (glycocholate [GC], taurocholate [TC], glycohenodeoxycholate [GCDC], and taurochenodeoxycholate [TCDC]), we obtained 6 bile-acid mixtures, each containing equal amounts of 2 bile acids (total bile acids [TBA], 2 mM). Changes in gluconeogenesis, ureagenesis, DNA contents, medium alanine aminotransferase, and morphologies were compared among the paired bile acid compositions by measuring the C/CDC ratio ([GC + TC]/[GCDC + TCDC]) of each. In terms of their relative impairments of ureagenesis from greatest to least, the acids were GCDC, TCDC, and GC, which was almost the same as TC. When the C/CDC ratio was 0, the values of all parameters measured deteriorated. When the C/CDC ratio was 1 in the presence of 1 mM GCDC, only the rate of ureagenesis was diminished. When the C/CDC ratio was infinite, no hepatocellular injury was observed. GCDC and TCDC, together or separately, showed significant hepatocellular injury when the TBA concentration was 2 mM.

Ursodeoxycholic acid may inhibit deoxycholic acid-induced apoptosis by modulating mitochondrial transmembrane potential and reactive oxygen species production

BACKGROUND

The hydrophilic bile salt ursodeoxycholate (UDCA) inhibits injury by hydrophobic bile acids and is used to treat cholestatic liver diseases. Interestingly, hepatocyte cell death from bile acid-induced toxicity occurs more frequently from apoptosis than from necrosis. However, both processes appear to involve the mitochondrial membrane permeability transition (MPT). In this study, we determined the inhibitory effect of UDCA on deoxycholic acid (DCA)-induced MPT in isolated mitochondria by measuring changes in transmembrane potential (delta psi m) and production of reactive oxygen species (ROS). In addition, we examined the expression of apoptosis-associated proteins in mitochondria isolated from livers of bile acid-fed animals.

MATERIALS AND METHODS

Adult male rats were maintained on standard diet supplemented with DCA and/or UDCA for 10 days. Mitochondria were isolated from livers by sucrose/percoll gradient centrifugation and MPT was measured using spectrophotometric and fluorimetric assays. delta psi m and ROS generation were determined by FACScan analysis. Cytoplasmic and mitochondrial protein abundance were determined by Western blot analysis.

RESULTS

DCA increased mitochondrial swelling 25-fold over controls (p < 0.001); UDCA reduced the swelling by > 40% (p < 0.001). Similarly, UDCA inhibited DCA-mediated release of calcein-loaded mitochondria by 50% (p < 0.001). delta psi m was significantly decreased in mitochondria incubated with DCA but not with UDCA. delta psi m disruption was followed closely by increased superoxide anion and peroxides production (p < 0.01). Coincubation of mitochondria with UDCA significantly inhibited the changes associated with DCA (p < 0.05). In vivo, DCA feeding was associated with a 4.5-fold increase in mitochondria-associated Bax protein levels (p < 0.001); combination feeding with UDCA almost totally inhibited this increase (p < 0.001).

CONCLUSION

UDCA significantly reduces DCA-induced disruption of delta psi m, ROS production, and Bax protein abundance in mitochondria, suggesting both short- and long-term mechanisms in preventing MPT. The results suggest a possible role for UDCA as a therapeutic agent in the treatment of both hepatic and nonhepatic diseases associated with high levels of apoptosis.

Extrahepatic deposition and cytotoxicity of lithocholic acid: studies in two hamster models of hepatic failure and in cultured human fibroblasts

Effects of bile acids on tissues outside of the enterohepatic circulation may be of major pathophysiological significance under conditions of elevated serum bile acid concentrations, such as in hepatobiliary disease. Two hamster models of hepatic failure, namely functional hepatectomy (HepX), and 2-day bile duct ligation (BDL), as well as cultured human fibroblasts, were used to study the comparative tissue uptake, distribution, and cytotoxicity of lithocholic acid (LCA) in relation to various experimental conditions, such as binding of LCA to low-density lipoprotein (LDL) or albumin as protein carriers. Fifteen minutes after i.v. infusion of [24-(14)C]LCA, the majority of LCA in sham-operated control animals was recovered in liver, bile, and small intestine. After hepatectomy, a significant increase in LCA was found in blood, muscle, heart, brain, adrenals, and thymus. In bile duct-ligated animals, significantly more LCA was associated with blood and skin, and a greater than twofold increase in LCA was observed in the colon. In the hepatectomized model, the administration of LCA bound to LDL resulted in a significantly higher uptake in the kidneys and skin. The comparative time- and concentration-dependent uptake of [14C]LCA, [14C]chenodeoxycholic acid (CDCA), and [14C]cholic acid (CA) in cultured human fibroblasts was nonsaturable and remained a function of concentration. Initial rates of uptake were significantly increased by approximately tenfold, with decreasing hydroxylation of the respective bile acid. After 1 hour of exposure of fibroblasts to LCA, there was a significant, dose-dependent decrease in mitochondrial dehydrogenase activity from 18% to 34% of the control, at LCA concentrations ranging from 1 to 20 micromol/L. At a respective concentration of 100 and 700 micromol/L, CDCA caused a 35% and 99% inhibition of mitochondrial dehydrogenase activity. None of the bile acids tested, with the exception of 700 micromol/L CDCA, caused a significant release of cytosolic lactate dehydrogenase into the medium. In conclusion, we show that bile acids selectively accumulate in nonhepatic tissues under two conditions of impaired liver function. Furthermore, the extrahepatic tissue distribution of bile acids during cholestasis may be affected by serum lipoprotein composition. At a respective concentration of 1 and 100 micromol/L, LCA and CDCA induced mitochondrial damage in human fibroblasts, after just 1 hour of exposure. Therefore, enhanced extrahepatic uptake of hydrophobic bile acids during liver dysfunction, or disorders of lipoprotein metabolism, may have important implications for bile-acid induced cytotoxic effects in tissues of the systemic circulation.

Vitamin E reduces oxidant injury to mitochondria and the hepatotoxicity of taurochenodeoxycholic acid in the rat

BACKGROUND & AIMS

Hydrophobic bile acids have been implicated in the pathogenesis of cholestatic liver injury. The hypothesis that hydrophobic bile acid toxicity is mediated by oxidant stress in an in vivo rat model was tested in this study.

METHODS

A dose-response study of bolus intravenous (i.v.) taurochenodeoxycholic acid (TCDC) in rats was conducted. Rats were then pretreated with parenteral alpha-tocopherol, and its effect on i.v. TCDC toxicity was evaluated by liver blood tests and by assessing mitochondrial lipid peroxidation.

RESULTS

Four hours after an i.v. bolus of TCDC (10 mumol/100 g weight), serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels peaked, hepatic mitochondria showed evidence of increased lipid peroxidation, and serum bile acid analysis was consistent with a cholestatic injury. Liver histology at 4 hours showed hepatocellular necrosis and swelling and mild portal tract inflammation. Treatment with parenteral alpha-tocopherol was associated with a 60%-70% reduction in AST and ALT levels, improved histology, and a 60% reduction in mitochondrial lipid peroxidation in rats receiving TCDC.

CONCLUSIONS

These data show that hepatocyte injury and oxidant damage to mitochondria caused by i.v. TCDC can be significantly reduced by pretreatment with the antioxidant vitamin E. These in vivo findings support the role for oxidant stress in the pathogenesis of bile acid hepatic toxicity.

Apoptosis induced in rat hepatocytes by in vivo exposure to taurochenodeoxycholate

Enzymatic and molecular cytochemistry was used to detect and follow the hepatotoxic effects caused in overnight-fasted Sprague-Dawley rats by a 1-h continuous intrafemoral infusion of taurochenodeoxycholate at 0.4 and 0.8 mumol-1 min-1 100 g-1 body weight dose levels. Rats were killed at 0, 1 and 24 h from the end of perfusion. Their livers were examined for morphology, DNA fragmentation (by a TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP-nick end-labelling assay), cell regeneration (by in vivo bromodeoxydurine incorporation), reduced glutathione, calcium and several enzyme cytochemical activities. Isolated injured hepatocytes randomly scattered throughout the liver were already evident at the end of perfusion. DNA fragmentation and cytoplasm shrinkage were prominent and early features of injured hepatocytes, which later showed calcium loading and chromatin clumping. Preserved cytochemical enzymatic activities indicated that plasma and mitochondria membranes were not severely damaged. Inflammatory response was absent. These observations indicate that an acute exposure to taurochenodeoxycholate induces a cell death process with apoptotic features.

Composition and concentration of bile acid reflux into the esophagus of patients with gastroesophageal reflux disease

BACKGROUND

Reflux of duodenal contents into the esophagus of patients with gastroesophageal reflux disease has been suggested by pH and bilirubin monitoring but is rarely directly measured. A portable device has been developed and was used to collect and quantitate material refluxed into the esophagus under ambulatory conditions during a prolonged time period. The objective of this study was to use this device to quantitate the composition and concentration of bile acids refluxed into the esophagus of patients with gastroesophageal reflux disease.

METHODS

Esophageal aspiration was performed on 43 normal subjects and 37 patients with reflux disease during a 17-hour period. Aspiration was performed through a modified 16F Salem sump tube, positioned 5 cm above the lower esophageal sphincter and connected to a portable, battery powered pump that aspirated continuously at 100 mm Hg pressure. Validation studies showed that minimal amounts of saliva and swallowed liquids were aspirated and that gastric pressure was not altered. Postprandial, upright, and supine collections were performed. Total bile acids were assayed by a standard enzymatic assay; specific conjugated bile acids were analyzed by high-performance liquid chromatography.

RESULTS

There was no difference in the total aspiration volume between normal volunteers and patients with gastroesophageal reflux disease, although patients tended to have a higher volume in the supine and postprandial periods. Bile acids could be detected in 58% of normal subjects and 86% of patients (p < 0.003). The mean concentration of bile salt exposure (micromole per liter) was higher in patients during the postprandial and supine periods. The mean bile acid reflux rate (micromole per hour) during all three aspiration periods was significantly higher in patients. On a molar basis the composition of the bile acids was 60% glycocholic acid, 16% glycodeoxycholic acid, and 15% glycochenodeoxycholic acid. Taurocholic, taurodeoxycholic, taurochenodeoxycholic, and glycolithocholic acid constituted the remaining 10%.

CONCLUSIONS

Patients with reflux disease have an increased concentration of bile acids in their esophageal aspirates. Most of the exposure occurs during the postprandial and supine periods. A variety of bile acids were detected, most of which were in their glycine conjugated form.

Hepatotoxicity of an HIV protease inhibitor in dogs and rats

Oral administration of the HIV protease inhibitor L-689,502 caused cholestasis and hepatocyte injury in rats and dogs. These changes occurred rapidly, with elevations in serum transaminase observed as early as 6 hr after oral dosing in dogs. The acute phase of this hepatotoxic response was characterized in more detail in rats. Following intravenous administration, bile flow was decreased in a dose-dependent manner with greater than 90% decrease in less than 30 min at a dose of 5 mg/kg. The decrease in bile flow was associated with a decrease in erythritol clearance. The decrease in bile flow was not due to disruption of biliary tight junctions. Sucrose clearance was not increased and biliary bile acid concentrations in treated animals were not different from controls. Unlike control animals, bile flow was not stimulated by infusion of the bile acid tauroursodeoxycholic acid in animals treated with L-689,502. These cholestatic effects may be due, in part, to direct hepatocyte injury. Histological examination of perfusion-fixed livers 30 min after L-689,502 administration revealed periportal changes including hepatocyte vacuolation and occasional single cell necrosis. On a subcellular level, the nucleus and mitochondria were intact in less-severely affected cells. However, extensive vacuolation with multilamellar inclusions was pronounced in these cells. In addition, canalicular ectasia was also observed which was consistent with the cholestatic changes that were seen. In summary, L-689,502 is a potent, rapid acting hepatotoxin in dogs and rats. The mechanism by which this agent induces cholestasis is novel compared to other well-characterized cholestatic agents such as alpha-naphtylisothiocyanate and ethinyl estradiol.

Vasopressin reduces taurochenodeoxycholate-induced hepatotoxicity by lowering the hepatocyte taurochenodeoxycholate content

BACKGROUND/AIMS

Vasopressin has been reported to reduce bile flow, but its effects on bile acid secretion and bile acid-related hepatotoxicity are still unclear. We therefore investigated the influence of vasopressin on the hepatotoxicity and biliary excretion of taurochenodeoxycholic acid in primary cultured rat hepatocytes and isolated perfused rat liver models.

METHODS/RESULTS

1) Addition of vasopressin to hepatocyte cultures significantly decreased lactate dehydrogenase release as compared to cultures exposed to 1 mM taurochenodeoxycholic acid alone, and also reduced intracellular taurochenodeoxycholic acid content from 19.3 +/- 2.2 to 13.0 +/- 1.6 nmol/mg protein. After 30 min of preincubation with 1 mM taurochenodeoxycholic acid, rinsing and reculture of hepatocytes in bile acid-free medium resulted in gradual decrease in the intracellular level of the bile acid, and addition of vasopressin (10(-9) M) to the reculture medium accelerated this process. 2) Superimposition of vasopressin (330 pmol/l) for 10 min on taurochenodeoxycholic acid infusion (1.0 mumol/min: 25 mumol/l) caused a rapid increase in bile flow and biliary excretion of taurochenodeoxycholic acid (697 +/- 42 vs 584 +/- 27 nmol/10 min per g liver) from perfused rat livers, and significantly reduced lactate dehydrogenase release. 3) Superimposition of the PKC blocker H-7 (5 mumol/l) on taurochenodeoxycholic acid infusion (1.0 mumol/min: 25 mumol/l) caused a gradual increase in bile flow and biliary excretion of taurochenodeoxycholic acid. Furthermore, an additional infusion of vasopressin (100 pmol/l) for 10 min in the presence of H-7 produced a greater increase in bile flow and biliary excretion of taurochenodeoxycholic acid as compared with H-7 alone (754 +/- 71 vs. 657 +/- 26 nmol/g liver). 4) Continuous infusion of vasopressin (330 pmol/l) significantly increased the late peak (10-50 min) of horseradish peroxidase excretion from perfused livers (from 8.48 +/- 1.02 to 21.7 +/- 6.02 ng/g liver).

CONCLUSIONS

These findings suggest that vasopressin exerts a protective effect against taurochenodeoxycholic acid-induced hepatotoxicity by stimulating the secretion of this bile acid via intracellular vesicular transport systems.

Effect of deoxycholic acid and ursodeoxycholic acid on lipid peroxidation in cultured macrophages

BACKGROUND

Kupffer cells are essential for normal hepatic homeostasis and when stimulated, they secrete reactive oxygen species, nitric oxide, eicosanoids, and cytokines. Some of these products are cytotoxic and attack nucleic acids, thiol proteins, or membrane lipids causing lipid peroxidation. Hydrophobic bile acids, such as deoxycholic acid (DCA), can damage hepatocytes by solubilising membranes and impairing mitochondrial function, as well as increasing the generation of reactive oxygen species.

OBJECTIVES

The hypothesis that hydrophobic bile acids could stimulate Kupffer cells to increase their capacity to generate reactive oxygen species by measuring cellular lipid peroxidation was tested. Because the hydrophilic bile acid, ursodeoxycholic acid (UDCA) can block hydrophobic bile acid induced cellular phenomena, it was also hypothesised that UDCA could antagonise macrophage activation by hydrophobic bile acids to blunt their capacity to generate reactive oxygen species.

METHODS

J-774A.1 murine macrophages were incubated for 24 hours with either 10(-5) M and 10(-4) M (final concentration) DCA alone, or 10(-4) M UDCA alone, or a mixture of 10(-4) M 1:1 molar ratio of DCA and UDCA. At the end of the incubation period, the culture medium was collected for determination of cellular lipid peroxidation by measuring the malondialdehyde (MDA) content in the medium with the thiobarbituric acid reactive substances assay.

RESULTS

10(-5) M and 10(-4) M DCA increased MDA generation by cultured macrophages. 10(-4) M UDCA alone did not increase MDA generation but blocked the peroxidative actions of DCA.

CONCLUSIONS

Hydrophobic bile acids, after their hepatic retention, can oxidatively activate Kupffer cells to generate reactive oxygen species. Because UDCA can block this action, the beneficial effect of UDCA is, in part, related to its ability to act as an antioxidant.

Effects of submicellar bile salt concentrations on biological membrane permeability to low molecular weight non-ionic solutes

Bile salts have been hypothesized to mediate cytotoxicity by increasing membrane permeability to aqueous solutes. We examined whether submicellar bile salt concentrations affect model and native membrane permeability to small uncharged molecules such as water, urea, and ammonia. Osmotic water permeability (Pf) and urea permeability were measured in large unilamellar vesicles composed with egg yolk phosphatidylcholine (EYPC) +/- cholesterol (Ch) or rat liver microsomal membranes by monitoring self-quenching of entrapped carboxyfluorescein (CF). Ammonia permeability was determined utilizing the pH dependence of CF fluorescence. Submicellar bile salt concentrations did not significantly alter Pf of EYPC +/- Ch or rat liver microsomal membranes. At taurodeoxycholate (TDC) or tauroursodeoxycholate concentrations approaching those that solubilized membrane lipids, CF leakage occurred from vesicles, but Pf remained unchanged. Higher bile salt concentrations (0.5-2 mM TDC) did not alter Pf of equimolar EYPC/Ch membranes. The activation energy for transmembrane water flux was unchanged (12.1 +/- 1.2 kcal/mol for EYPC) despite the presence of bile salts in one or both membrane hemileaflets, suggesting strongly that bile salts do not form transmembrane pores that facilitate water flux. Furthermore, submicellar bile salt concentrations did not increase membrane permeability to urea or ammonia. We conclude that at submicellar concentrations, bile salts do not form nonselective convective channels that facilitate transmembrane transport of small uncharged molecules. These results suggest that bile salt-mediated transport of specific substrates, rather than nonselective enhancement of membrane permeability, underlies bile salt cytotoxicity for enterocytes and hepatocytes.

Bile acids in the assessment of hepatocellular function

Bile acids, which are synthesized in the liver from cholesterol, are important in the production of bile flow, excretion of cholesterol, and intestinal digestion and absorption of fats and fat-soluble vitamins. Increases and/or alterations in concentrations of bile acids in serum are specific and sensitive indicators of hepatobiliary disorders. Synthesis of bile acids in hepatocytes involves steps in endoplasmic reticulum, cytosol, mitochondria, and peroxisomes. Other important hepatocellular processes involving bile acids include active uptake by the basolateral membrane, intracellular transport, P-450-mediated conjugations and hydroxylations, and canalicular secretion. Hydrophobic bile acids produce hepatotoxicity in vivo and in vitro. In experimental and epidemiologic studies, some of these forms have been identified as causative agents in the development of colon and liver (experimental only) cancer. Conversely, several hydrophilic forms, primarily ursodeoxycholic acid, have demonstrated cytoprotective properties in a variety of clinical and experimental hepatobiliary diseases and disorders. Because bile acids can have dramatically different properties and effects, determination of mechanisms of action of these compounds has become an active area of research. Primary isolated hepatocytes provide an opportunity to investigate bile acid-related functions and effects in well-designed, carefully controlled studies. Short-term cultures have been used to study a variety of issues related to bile acids, including cytotoxicity, synthesis, and hepatocellular processing. With these systems, however, many functions of mature hepatocytes, including those pertaining to bile acids, can be lost when cultures are maintained for more than several days. Recent developments in culture techniques permit long-term maintenance of functionally stable, differentiated cells. Pertaining to bile acid research, these systems remain to be fully characterized but, in appropriate situations, they should provide important alternatives to in vivo studies and short-term in vitro assays.

Mixed reflux of gastric and duodenal juices is more harmful to the esophagus than gastric juice alone. The need for surgical therapy re-emphasized

OBJECTIVE

The author's goal was to determine the role of duodenal components in the development of complications of gastroesophageal reflux disease.

SUMMARY AND BACKGROUND DATA

There is a disturbing increase in the prevalence of complications, specifically the development of Barrett's esophagus among patients with gastroesophageal reflux disease. Earlier studies using pH monitoring and aspiration techniques have shown that increased esophageal exposure to fluid with a pH above 7, that is, of potential duodenal origin, may be an important factor in this phenomenon.

METHODS

The presence of duodenal content in the esophagus was studied in 53 patients with gastroesophageal reflux disease confirmed by 24-hour pH monitoring. A portable spectrophotometer (Bilitec 2000, Synectics, Inc.) with a fiberoptic probe was used to measure intraluminal bilirubin as a marker for duodenal juice in the esophagus. Normal values for bilirubin monitoring were established for 25 healthy subjects. In a subgroup of 22 patients, a custom-made program was used to correlate simultaneous pH and bilirubin absorbance readings.

RESULTS

Fifty-eight percent of patients were found to have increased esophageal exposure to gastric and duodenal juices. The degree of mucosal damage increased when duodenal juice was refluxed into the esophagus, in that patients with Barrett's metaplasia (n = 27) had a significantly higher prevalence of abnormal esophageal bilirubin exposure than did those with erosive esophagitis (n = 10) or with no injury (n = 16). They also had a greater esophageal bilirubin exposure compared with patients without Barrett's changes, with or without esophagitis. The correlation of pH and bilirubin monitoring showed that the majority (87%) of esophageal bilirubin exposure occurred when the pH of the esophagus was between 4 and 7.

CONCLUSIONS

Reflux of duodenal juice in gastroesophageal reflux disease is more common than pH studies alone would suggest. The combined reflux of gastric and duodenal juices causes severe esophageal mucosal damage. The vast majority of duodenal reflux occurs at a pH range of 4 to 7, at which bile acids, the major component of duodenal juice, are capable of damaging the esophageal mucosa.

Mixed reflux of gastric and duodenal juices is more harmful to the esophagus than gastric juice alone. The need for surgical therapy re-emphasized

OBJECTIVE

The author's goal was to determine the role of duodenal components in the development of complications of gastroesophageal reflux disease.

SUMMARY AND BACKGROUND DATA

There is a disturbing increase in the prevalence of complications, specifically the development of Barrett's esophagus among patients with gastroesophageal reflux disease. Earlier studies using pH monitoring and aspiration techniques have shown that increased esophageal exposure to fluid with a pH above 7, that is, of potential duodenal origin, may be an important factor in this phenomenon.

METHODS

The presence of duodenal content in the esophagus was studied in 53 patients with gastroesophageal reflux disease confirmed by 24-hour pH monitoring. A portable spectrophotometer (Bilitec 2000, Synectics, Inc.) with a fiberoptic probe was used to measure intraluminal bilirubin as a marker for duodenal juice in the esophagus. Normal values for bilirubin monitoring were established for 25 healthy subjects. In a subgroup of 22 patients, a custom-made program was used to correlate simultaneous pH and bilirubin absorbance readings.

RESULTS

Fifty-eight percent of patients were found to have increased esophageal exposure to gastric and duodenal juices. The degree of mucosal damage increased when duodenal juice was refluxed into the esophagus, in that patients with Barrett's metaplasia (n = 27) had a significantly higher prevalence of abnormal esophageal bilirubin exposure than did those with erosive esophagitis (n = 10) or with no injury (n = 16). They also had a greater esophageal bilirubin exposure compared with patients without Barrett's changes, with or without esophagitis. The correlation of pH and bilirubin monitoring showed that the majority (87%) of esophageal bilirubin exposure occurred when the pH of the esophagus was between 4 and 7.

CONCLUSIONS

Reflux of duodenal juice in gastroesophageal reflux disease is more common than pH studies alone would suggest. The combined reflux of gastric and duodenal juices causes severe esophageal mucosal damage. The vast majority of duodenal reflux occurs at a pH range of 4 to 7, at which bile acids, the major component of duodenal juice, are capable of damaging the esophageal mucosa.

Human cholangiocarcinomas express somatostatin receptors and respond to somatostatin with growth inhibition

BACKGROUND/AIMS

Cholangiocarcinoma, a malignancy of biliary epithelia, is usually fatal because of absence of tests for early detection and lack of effective therapy. Somatostatin (SS) receptors are expressed in several malignancies and in rodent biliary epithelia. We tested the hypothesis that SS receptors are present in cholangiocarcinomas.

METHODS

We examined tissue from seven surgically resected human cholangiocarcinomas and a human bile duct cancer cell line for the messenger RNA for one subtype of SS receptors (SSTR2) and studied binding and growth-active properties of SS and its analogues.

RESULTS

SSTR2 messenger RNA was expressed in all seven human cholangiocarcinoma specimens. Experiments with the human cholangiocarcinoma cell line showed specific, saturable binding of an SS analogue (MK-678) with high affinity for SSTR2 on cholangiocarcinoma membranes; inhibition in vitro of tumor cell proliferation by SS-14 and its analogue, octreotide; and inhibition in vivo of tumor growth in athymic mice implanted with human cholangiocarcinoma cells and treated with lanreotide, another SS analogue. Experiments to elucidate a possible mechanism of growth inhibition by SS showed it was not through changes in cellular cyclic adenosine monophosphate or calcium levels. Using gamma camera imaging with an 111In-SS analogue, we localized a histologically proven cholangiocarcinoma in a patient.

CONCLUSIONS

These results suggest that SS analogues may be useful for diagnostic localization and treatment of biliary tract malignancies.

Bile acids in the diagnosis, pathology, and therapy of hepatobiliary diseases

Bile acids are normally confined in the enterohepatic circulation in which they play an important role in bile formation, biliary lipid excretion, and intestinal lipid absorption. In hepatobiliary diseases, bile acids escape the confinement of the enterohepatic circulation, allowing the measurement of the serum total bile acid concentration as a diagnostic indicator. Accumulation of certain bile acids within the hepatocyte, amplified as a consequence of cholestatic hepatobiliary disease, probably enhances cytotoxicity and leads to secondary pathology. Ursodeoxycholate, a bile acid with atypical physiological effects, may be useful in the treatment of various long-term cholestatic hepatobiliary diseases. Presently, most of the information on the toxicity and therapeutic usefulness of bile acids are based on studies in humans and experimental animals. Further studies, both basic and clinical, are needed to determine the pathologic as well as the therapeutic effects of bile acids in domestic animals.

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

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

Liver cell necrosis: cellular mechanisms and clinical implications

Based on our current understanding, we have developed a provisional model for hepatocyte necrosis that may be applicable to cell necrosis in general (Figure 6). Damage to mitochondria appears to be a key early event in the progression to necrosis. At least two pathways may be involved. In the first, inhibition of oxidative phosphorylation in the absence of the MMPT leads to ATP depletion, ion dysregulation, and enhanced degradative hydrolase activity. If oxygen is present, toxic oxygen species may be generated and lipid peroxidation can occur. Subsequent cytoskeleton and plasma membrane damage result in plasma membrane bleb formation. These steps are reversible if the insult to the cell is removed. However, if injury continues, bleb rupture and cell lysis occur. In the second pathway, mitochondrial damage results in an MMPT. This step is irreversible and leads to cell death by as yet uncertain mechanisms. It is important to note that MMPT may occur secondary to changes in the first pathway (e.g. oxidative stress, increased Cai2+, and ATP depletion) and that all the "downstream events" occurring in the first pathway may result from MMPT (e.g., ATP depletion, ion dysregulation, or hydrolase activation). Proof of this model's applicability to cell necrosis in general awaits further validation. In this review, we have attempted to highlight the advances in our understanding of the cellular mechanisms of necrotic injury. Recent advances in this understanding have allowed scientists and clinicians a better comprehension of liver pathophysiology. This knowledge has provided new avenues of therapy and played a key role in the practice of hepatology as evidenced by advances in organ preservation. Understanding the early reversible events leading to cellular and subcellular damage will be key to prevention and treatment of liver disease. Hopefully, disease and injury specific preventive or pharmacological strategies can be developed based on this expanding data base.

Inhibition of mitochondrial beta-oxidation as a mechanism of hepatotoxicity

Severe and prolonged impairment of mitochondrial beta-oxidation leads to microvesicular steatosis, and, in severe forms, to liver failure, coma and death. Impairment of mitochondrial beta-oxidation may be either genetic or acquired, and different causes may add their effects to inhibit beta-oxidation severely and trigger the syndrome. Drugs and some endogenous compounds can sequester coenzyme A and/or inhibit mitochondrial beta-oxidation enzymes (aspirin, valproic acid, tetracyclines, several 2-arylpropionate anti-inflammatory drugs, amineptine and tianeptine); they may inhibit both mitochondrial beta-oxidation and oxidative phosphorylation (endogenous bile acids, amiodarone, perhexiline and diethylaminoethoxyhexestrol), or they may impair mitochondrial DNA transcription (interferon-alpha), or decrease mitochondrial DNA replication (dideoxynucleoside analogues), while other compounds (ethanol, female sex hormones) act through a combination of different mechanisms. Any investigational molecule should be screened for such effects.

Ursodeoxycholate protects oxidative mitochondrial metabolism from bile acid toxicity: dose-response study in isolated rat liver mitochondria

The effect of ursodeoxycholate and tauroursodeoxycholate on the toxicity of lipophilic bile acids (chenodeoxycholate and lithocholate) on the function of the electron transport chain was investigated in isolated rat liver mitochondria. At a concentration of 30 mumol/L, both chenodeoxycholate and lithocholate reduced state 3 oxidation rates and respiratory control ratios of L-glutamate, succinate and duroquinol. In contrast, ADP/O ratios of these substrates and oxidative metabolism of ascorbate were not significantly affected. Ursodeoxycholate did not impair mitochondrial oxidative metabolism up to concentrations of 100 mumol/L; at 300 mumol/L, however, it decreased state 3 oxidation rates and respiratory control ratios of L-glutamate, succinate and duroquinol. Tauroursodeoxycholate had no significant inhibitory effect on state 3 oxidation rates of L-glutamate and succinate at concentrations up to 300 mumol/L. When ursodeoxycholate (final concentration, 30 mumol/L or 100 mumol/L) was added to mitochondrial incubations containing chenodeoxycholate or lithocholate, the toxic effects of lipophilic bile acids on mitochondrial oxidative metabolism were partially reversed. However, 300 mumol/L ursodeoxycholate, in combination with chenodeoxycholate or lithocholate, exhibited greater toxicity compared with incubations containing only the individual bile acids. In contrast to ursodeoxycholate, tauroursodeoxycholate did not reduce the toxic effects of chenodeoxycholate or lithocholate on mitochondrial metabolism. Ursodeoxycholate (100 mumol/L) significantly decreased the incorporation of chenodeoxycholate into mitochondrial membranes, whereas the decrease in lithocholate incorporation was not statistically significant. These studies demonstrate that ursodeoxycholate, but not tauroursodeoxycholate, decreases the toxicity of lipophilic bile acids on the function of the electron but increases bile acid-induced mitochondrial toxicity at higher concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Increases of intracellular magnesium promote glycodeoxycholate-induced apoptosis in rat hepatocytes

Retention of bile salts by the hepatocyte contributes to liver injury during cholestasis. Although cell injury can occur by one of two mechanisms, necrosis versus apoptosis, information is lacking regarding apoptosis as a mechanism of cell death by bile salts. Our aim was to determine if the bile salt glycodeoxycholate (GDC) induces apoptosis in rat hepatocytes. Morphologic assessment included electron microscopy and quantitation of nuclear fragmentation by fluorescent microscopy. Biochemical studies included measurements of DNA fragmentation, in vitro endonuclease activity, cytosolic free Ca2+ (Cai2+), and cytosolic free Mg2+ (Mgi2+). Morphologic studies demonstrated typical features of apoptosis in GDC (50 microM) treated cells. The "ladder pattern" of DNA fragmentation was also present in DNA obtained from GDC-treated cells. In vitro endonuclease activity was 2.5-fold greater with Mg2+ than Ca2+. Although basal Cai2+ values did not change after addition of GDC, Mgi2+ increased twofold. Incubation of cells in an Mg(2+)-free medium prevented the rise in Mgi2+ and reduced nuclear and DNA fragmentation. In conclusion, GDC induces apoptosis in hepatocytes by a mechanism promoted by increases of Mgi2+ with stimulation of Mg(2+)-dependent endonucleases. These data suggest for the first time that changes of Mgi2+ may participate in the program of cellular events culminating in apoptosis.

Ursodeoxycholate conjugates protect against disruption of cholesterol-rich membranes by bile salts

BACKGROUND/AIMS

Ursodeoxycholic acid attenuates hepatocellular injury in cholestatic disorders, possibly by counteracting membrane disruptive effects of endogenous bile salts. The possible physicochemical basis of this protective effect was explored by using model membranes composed of egg phosphatidylcholine and cholesterol.

METHODS

Large unilamellar vesicles containing trapped 3H inulin were prepared by extrusion and gel filtration. Vesicle disruption (release of trapped inulin) was quantified using rapid centrifugal ultrafiltration.

RESULTS

Disruption of membranes increased with bile salt concentration, hydrophobicity, and increasing ionic strength. Disruption decreased with a decreasing bile salt/phospholipid ratio or an increasing cholesterol/phospholipid ratio. Vesicle disruption by taurodeoxycholate (3 alpha, 12 alpha-dihydroxy-5 beta-cholanoyl taurine) was reduced in a concentration-dependent manner by addition of tauroursodeoxycholate (3 alpha,7 beta-dihydroxy-5 beta-cholanoyl taurine) (TUDC) when the cholesterol/phospholipid ratio was > or = 0.5, but TUDC was not protective at a cholesterol/phospholipid ratio < or = 0.2. Glycoursodeoxycholate (3 alpha,7 beta-dihydroxy-5 beta-cholanoyl glycine) was somewhat less protective than TUDC, and unconjugated ursodeoxycholate (3 alpha,7 beta-dihydroxy-5 beta-cholanoate) (UDC) had little effect. Taurine conjugates of several other hydrophilic bile salts were also protective, but protection was not strictly proportional to hydrophilicity.

CONCLUSIONS

Conjugates of UDC and other hydrophilic bile salts can reduce disruption of cholesterol-rich model membranes by more toxic bile salts via a purely physicochemical mechanism. UDC conjugates in vivo may protect the cholestatic liver by preventing bile salt disruption of the cholesterol-rich canalicular membrane.