Comparison of the effects of bile acids on cell viability and DNA synthesis by rat hepatocytes in primary culture

Bile acid-induced inhibition of DNA synthesis by the regenerating rat liver in the absence of other manifestation of impairment in liver cell viability has been reported. Because in experiments carried out on in vivo models bile acids are rapidly taken up and secreted into bile, it is difficult to establish steady concentrations to which the hepatocytes are exposed. Thus, in this work, a dose-response study was carried out to investigate the in vitro cytotoxic effect of major unconjugated and tauro- (T) or glyco- (G) conjugated bile acids and to compare this as regards their ability to inhibit DNA synthesis. Viability of hepatocytes in primary culture was measured by Neutral red uptake and formazan formation after 6 h exposure of cells to bile acids. The rate of DNA synthesis was determined by radiolabeled thymidine incorporation into DNA. Incubation of hepatocytes with different bile acid species - cholic acid (CA), deoxycholic acid (DCA), chenodeoxycholic acid (CDCA) and ursodeoxycholic acid (UDCA), in the range of 10-1000 microM - revealed that toxicity was stronger for the unconjugated forms of CDCA and DCA than for CA and UDCA. Conjugation markedly reduced the effects of bile acids on cell viability. By contrast, the ability to inhibit radiolabeled thymidine incorporation into DNA was only slightly lower for taurodeoxycholic acid (TDCA) and glycodeoxycholic acid (GDCA) than for DCA. When the effect of these bile acids on DNA synthesis and cell viability was compared, a clear dissociation was observed. Radiolabeled thymidine incorporation into DNA was significantly decreased (-50%) at TDCA concentrations at which cell viability was not affected. Lack of a cause-effect relationship between both processes was further supported by the fact that well-known hepatoprotective compounds, such as tauroursodeoxycholic acid (TUDCA) and S-adenosylmethionine (SAMe) failed to prevent the effect of bile acids on DNA synthesis. In summary, our results indicate that bile acid-induced reduction of DNA synthesis does not require previous decreases in hepatocyte viability. This suggests the existence of a high sensitivity to bile acids of cellular mechanisms that may affect the rate of DNA repair and/or proliferation, which is of particular interest regarding the role of bile acids in the etiology of certain types of cancer.

Ethyl pyruvate improves survival and ameliorates distant organ injury in rats with severe acute pancreatitis

OBJECTIVE

To evaluate the effect of ethyl pyruvate (EP) in improving the survival and ameliorating distant organ damage and to investigate the role of high-mobility group box (HMGB) 1 in rats with established severe acute pancreatitis (SAP).

METHODS

Severe acute pancreatitis was induced by retrograde infusion of sodium taurodeoxycholate (5%, 1 mL/kg) into the biliopancreatic ducts in male Wistar rats. The rats were infused intravenously with EP of 40 mg/kg, 4 mg/kg, and 0.4 mg/kg initiating 12 hours, and EP of 40 mg/kg was administered beginning 2 hours before surgery (-2 hours) and 12, 24, and 36 hours after induction of SAP; then, the mortality was recorded. Serum tumor necrosis factor alpha, interleukin (IL) 6, and IL-1beta were measured using enzyme-linked immunosorbent assay. High-mobility group box 1 levels were measured using Western immunoblotting analysis.

RESULTS

Serum HMGB1 levels were increased dramatically after 12 hours, remained at high levels for 72 hours, and were significantly higher in rats with SAP than in those with mild and moderate pancreatitis (P < 0.01). Treatment with EP (40 mg/kg) conferred protection from lethality of SAP (EP survival [63%] vs vehicle survival [6.3%]; P < 0.001). No survival advantage occurred when treatment was initiated 36 hours after surgery, but administration beginning 2 hours before operation (-2 hours) and 12 and 24 hours after induction of SAP significantly increased survival. Ethyl pyruvate treatment significantly decreased serum HMGB1, tumor necrosis factor alpha, IL-1beta, and IL-6 levels and ameliorated extrapancreatic organ dysfunction in rats with SAP.

CONCLUSIONS

Ethyl pyruvate improves survival and ameliorates distant organ injury of SAP. These beneficial effects of EP are because of the modulation of HMGB1 and other inflammatory cytokine responses.

Evaluation of acute and subacute toxicity of sodium taurodeoxycholate in rats

Taurodeoxycholate (TDCA) inhibits various inflammatory responses suggesting potential clinical application. However, the toxicity of TDCA has not been evaluated in detail in vivo. We investigated the acute toxicity and 4-week repeated-dose toxicity of TDCA following intravenous infusion under Good Laboratory Practice regulations. In the sighting study of acute toxicity, one of two rats (one male and one female) treated with 300 mg/kg TDCA died with hepatotoxicity, suggesting that the approximate 50% lethal dose of TDCA is 300 mg/kg. Edema and discoloration were observed at the injection sites of tails when rats were infused with 150 mg/kg or higher amount of TDCA once. In 4-week repeated-dose toxicity study, no treatment-related mortality or systemic changes in hematology and serum biochemistry, organ weights, gross pathology, or histopathology were observed. However, the tail injection site showed redness, discharge, hardening, and crust formation along with histopathological changes such as ulceration, edema, fibrosis, and thrombosis when rats were infused with 20 mg/kg TDCA. Taken together, TDCA induced no systemic toxicity or macroscopic lesions at the injection site at a dose of 10 mg/kg/day, which is 33 times higher than the median effective dose observed in a mouse sepsis model. These findings suggest that TDCA might have a favorable therapeutic index in clinical applications.

Comparative cytotoxic and cytoprotective effects of taurohyodeoxycholic acid (THDCA) and tauroursodeoxycholic acid (TUDCA) in HepG2 cell line

This study was performed to compare the effects of two hydrophilic bile acids, taurohyodeoxycholic acid (THDCA) and tauroursodeoxycholic acid (TUDCA), on HepG2 cells. Cytotoxicity was evaluated at different times of exposure by incubating cells with increasing concentrations (50-800 micromol/l) of either bile acid, while their cytoprotective effect was tested in comparison with deoxycholic acid (DCA) (350 micromol/l and 750 micromol/l)-induced cytotoxicity. Culture media, harvested at the end of each incubation period, were analyzed to evaluate aspartate transaminase (AST), alanine transaminase and gamma-glutamyltranspeptidase release. In addition, the hemolytic effect of THDCA and TUDCA on human red blood cells was also determined. At 24 h of incubation neither THDCA nor TUDCA was cytotoxic at concentrations up to 200 and 400 micromol/l. At 800 micromol/l both THDCA and TUDCA induced a slight increase in AST release. At this concentration and with time of exposure prolonged up to 72 h, THDCA and TUDCA induced a progressive increase of AST release significantly (P<0.05) higher than that of controls being AST values for THDCA (2.97+/-0.88 time control value (tcv) at 48 h and 4.50+/-1.13 tcv at 72 h) significantly greater than those of TUDCA (1.50+/-0.20 tcv at 48 h and 1.80+/-0.43 tcv at 72 h) (P<0.01). In cytoprotection experiments, the addition of 50 micromol/l THDCA decreased only slightly (-5%) AST release induced by 350 micromol/l DCA, while the addition of 50 micromol/l TUDCA was significantly effective (-23%; P<0.05). Higher doses of THDCA or TUDCA did not reduce toxicity induced by 350 micromol/l DCA, but were much less toxic than an equimolar dose of DCA alone. At the concentration used in this experimental model neither THDCA nor TUDCA was hemolytic; however at a very high concentration (6 mmol/l) both bile acids induced 5-8% hemolysis. We conclude that bile acid molecules with a similar degree of hydrophilicity may show different cytotoxic and cytoprotective properties.

Acute effects of bile acids on the pancreatic duct epithelium in vitro

BACKGROUND

Acute pancreatitis is associated with passage of gallstones, although the mechanism(s) linking the two processes remains undefined. Bile reflux into the pancreatic duct could play a role but the experimental conditions often employed to induce pancreatitis rarely develop clinically. Here we examined whether low concentrations of bile affect ductal electrophysiology as an indirect measure of ductal epithelial integrity and function in vitro.

METHODS

The main duct was dissected out of freshly harvested bovine pancreata, cut into 1- x 2-cm sections, placed in tissue culture for 48-72 h, then placed in Ussing chambers. Changes in tissue resistance (Rt) and short-circuit current (Isc) were monitored. The responses to forskolin and bile (taurodeoxycholic acid, TDCA) were examined separately and together.

RESULTS

Forskolin (10 microM) produced a decrease in the Isc without a significant change in Rt, suggesting a secretory response, followed by a return to baseline. TDCA caused a similarly reversible decrease in the Isc at low doses, but a persistent drop at higher concentrations. A concurrent drop in Rt was noted at all TDCA concentrations, the duration of which correlated with dosage and degree of histological damage. Prior exposure to low (0.5 mM) doses of TDCA significantly blunted the response to subsequent forskolin challenge.

CONCLUSIONS

Acute exposure to TDCA in vitro causes epithelial damage at levels lower than those normally used to induce experimental pancreatitis. At the lower concentrations, Rt returns to baseline rapidly, suggesting recovery (restitution) from epithelial damage but with a persistent loss of the response to forskolin. Reflux of minute amounts of bile into the pancreatic duct could play a significant role in the pathogenesis of gallstone pancreatitis by uncoupling the normal stimulus-secretion apparatus of the ductal system and breaking down the epithelial barrier.

The pancreatic duct epithelium in vitro: bile acid injury and the effect of epidermal growth factor

BACKGROUND

Pancreatic duct epithelial cells form a barrier against parenchymal injury. The capacity of these cells to respond to injury has not been investigated. We hypothesized that epidermal growth factor (EGF), normally found in pancreatic juice, could protect the duct epithelium from damage.

METHODS

An explant system of duct cell culture developed in our lab with the bovine main pancreatic duct was used. Explants were exposed to bile acid (taurodeoxycholic acid [TDCA] 0, 0.05, 0.5, and 1 mmol/L) in the presence or absence of EGF (0, 1, 10, and 100 nmol/L) for 48 hours. Epithelial proliferation, damage, and growth out from the explant edge were assessed histologically. Expression of ductal markers and the extent of cell proliferation were determined by immunohistochemistry using specific antibodies.

RESULTS

Explant duct cells proliferated and demonstrated continued expression of key duct antigens in culture. TDCA produced dose-dependent mucosal damage and reduced epithelial density and growth from the edge. EGF increased cellular density in the native epithelium, but did not significantly alter growth from the edge. Mucosal damage created by TDCA exposure was significantly decreased with EGF and both growth from the edge and cell density were preserved.

CONCLUSIONS

Explants created from the bovine main pancreatic duct serve as an excellent model for the study of duct epithelial cells in vitro. These cells proliferate in response to EGF and are damaged by TDCA at concentrations below those normally associated with detergent-like activity and below levels observed in bile and duodenal secretions. The ability of EGF to protect from this injury suggests a potential physiologic role in the maintenance of the pancreatic duct mucosal barrier.

Nonclinical toxicology studies with sodium taurodeoxycholate: acute and subacute toxicity in dogs

Sodium taurodeoxycholate (TDCA) has been investigated for various inflammatory disorders such as sepsis. We recently evaluated nonclinical safety profile of TDCA using rats infused intravenously. As a series of preclinical safety investigations, we further conducted toxicity studies with TDCA delivered to dogs via intravenous administration under Good Laboratory Practice regulation in this study. In dose range-finding study (dose escalation study), dogs given with TDCA at a dose of 150 mg/kg showed marked changes in clinical signs, hematology, and serum biochemistry. And biochemical markers of liver damage and local skin lesions were observed following intravenous infusion of 100 mg/kg TDCA, suggesting that 100 mg/kg was chosen as the highest dose of TDCA for 4-week repeated-dose toxicity study using dogs. Despite no treatment-related significant changes in body weight, food consumption, ophthalmoscopy, and urinalysis, skin lesions were observed at the injection site of animals administered with higher than 50 mg/kg of TDCA along with biochemical and histopathological changes associated with liver injury. However, most of off-target effects were found to be reversible since these were recovered after stopping TDCA infusion. These findings indicate that the no-observed-adverse-effect-level (NOAEL) for TDCA in dogs was considered to be 5 mg/kg/d. Taken together, our results provide important toxicological profiles regarding the safe dose of TDCA for drug development or clinical application.

Co-mutagenicity of glyco- and tauro-deoxycholic acids in the Ames test

Mutagenicity and co-mutagenicity of glyco- and tauro-deoxycholic acids (GDCA and TDCA), which are abundant in human bile, were examined by the Ames test. The two chemicals were not mutagenic for themselves to Salmonella typhimurium TA98 and TA100, with and without S9 mix. They enhanced, however, the mutagenic activities of the pro-mutagens, 2-aminoanthracene (2AA) and benzo[a]pyrene (BaP), for both TA98 and TA100 with S9 mix. They were more co-mutagenic for the pro-mutagens on TA98 than on TA100. On TA98, the mutagenic activities of 2AA with GDCA (5 mumol/plate) and with TDCA (5 mumol/plate) were 9.7-fold and 11.8-fold as high as that of the corresponding control (2AA only), respectively. BaP with GDCA (2.5 mumol/plate) and with TDCA (2.5 mumol/plate) showed 2.8-fold and 3.0-fold increases over the corresponding control level (BaP only), respectively. It is hence concluded that GDCA and TDCA may enhance the activity of some mutagens existing in bile.

Taurodeoxycholate-induced intestinal injury is modulated by oxidative stress-dependent pre-conditioning like mechanisms

Mechanisms by which hydrophobic bile salts cause tissue changes below their critical micellar concentration (CMC, 1-2mM) and above (4-8mM) remain poorly understood. In this study, rat colonic mucosa was exposed to different concentrations of taurodeoxycholate (TDC), t-butyl-hydroperoxide (t-BH) or glutathione ester with or without pre-incubation with 2mM TDC. Exposure to 2mM TDC was associated with 10% higher tissue levels of total glutathione (GSH, basal values: 33.7+/-3.3 nmol/mg prot). With TDC 8mM, GSH decreased to 16.4+/-2.3 nmol/mg prot (P<0.05), oxidized glutathione (GSSG) increased by 60% (P<0.05), glutathione peroxidase (GSH-Px) and reductase activities were threefold increased, protein carbonyls fourfold increased, protein sulfhydrils decreased by 78%, lactate dehydrogenase (LDH) and GSSG release in the incubation medium were sixfold higher. In 2mM TDC pre-treated tissues, the subsequent incubation with 8mM TDC induced a lower loss of tissue GSH, and a lower release of LDH and GSSG. Pre-incubation with 2mM TDC partly protected against t-BH toxicity, while glutathione ester protected against 8mM TDC toxicity. In conclusion, TDC exposure causes opposite effects depending on CMC: induction of antioxidant protective systems including glutathione system (pre-conditioning effect) was observed with TDC below CMC, oxidative damages pointing to decreased mucosal detoxification potential with above CMC.

Acute taurodeoxycholate-induced pancreatitis in the rat is associated with hyperCCKemia

BACKGROUND

Cholecystokinin (CCK) has been suggested to be involved in the development and course of acute pancreatitis. In the present study we measured plasma CCK concentrations in acute experimental pancreatitis (AEP) in the rat, and evaluated the role of circulating CCK levels on the initial pancreatic damage in pancreatitis.

METHODS

Endogenous hyperCCKemia was induced by surgical biliodigestive shunt (BDS) and exogenous hyperCCKemia by infusion of CCK-8S. The CCK-A receptor antagonist devazepide was used to antagonize the effect of CCK. Pancreatitis was induced by pancreatic duct infusion of sodium taurodeoxycholate 4 wk after the BDS operation or 1 wk after the start of the infusions. Nonpancreatitic sham- and BDS-operated rats, respectively, were used as control animals as were groups of otherwise untreated rats with pancreatitis. The animals were sacrificed 6 h after induction of pancreatitis. Concentrations of CCK were determined in plasma as were protein and amylase levels in the pancreas and peritoneal exudates. The extent of pancreatic necroses was assessed microscopically.

RESULTS

Pancreatitis caused an 11-20-fold increase of circulating CCK as measured after 6 h. In pancreatitic rats with induced hyperCCKemia, there was a further marked increase of plasma CCK. Pancreatic weight and edema, protein and amylase contents, and extent of necroses were the same regardless of the level of plasma CCK. Devazepide had no influence on the studied pancreatic parameters.

CONCLUSION

We conclude that acute taurodeoxycholate-induced pancreatitis in the rat is associated with elevated plasma CCK concentrations. There seems, however, not to be any correlation between the degree of hyperCCKemia and the extent of initial pancreatic damage.

Reproductive toxicity of taurohyodeoxycholic acid

The reproductive toxicity of taurohyodeoxycholic acid (3 alpha, 6 alpha-dihydroxy-5-beta-cholanoyl-2-amino-ethyl-sulfonic acid, THDCA, Io, Praxis, CAS 2958-04-5), a new synthetized biliary acid patented in Europe, Japan and the United States for prevention and therapy of gallstones and related symptoms, was assayed by performing segment I (fertility and general reproductive performance) and segment II (teratology) studies. In the first study THDCA was administered (100, 220 or 500 mg/kg by oral route) to male and female rats prior to and in the early stage of pregnancy. No adverse effects or dose-related abnormalities were observed in the reproductive performance of either sex; no death or evidence of teratogenicity in fetuses were also observed. In the second study THDCA was administered (100, 220 or 500 mg/kg by oral route) to rats and rabbits during the fetal organogenesis period. No maternal toxicity, teratogenicity or adverse effects on growth of embryos and fetuses and no reduction of the viability index were observed. From these studies the no-effect dose can be estimated at 500 mg/kg.

Chronic toxicity of taurohyodeoxycholic acid in rats

Fifty-two-week oral toxicity and 24-week intraperitoneal toxicity of a new synthetized biliary acid, taurohyodeoxycholic acid (Io, Praxis, CAS 2958-04-5), were investigated in rats. Taurohyodeoxycholic acid was orally administered at dose levels up to 500 mg/kg/d and intraperitoneally administered at dose levels up to 200 mg/kg/d. The treated animals showed no deviations from normality in mortality, physical appearance and general behavior. Food and water consumption and body weight gain of the treated groups did not differ from those of the control. No treatment-related changes were observed in hematology, serum biochemistry, urinalysis, organ weights and post-mortem macroscopic or histopathological examinations. No dose- or sex-related differences were observed. The no-effect dose level was estimated to be 500 mg/kg/d in the chronic oral toxicity study and 200 mg/kg/d in the intraperitoneal study.

Chronic toxicity of taurohyodeoxycholic acid in dogs

Fifty-two-week oral toxicity and 24-week intramuscular toxicity of a new synthetized biliary acid, taurohyodeoxycholic acid (Io, Praxis, CAS 2958-04-5) were investigated in dogs. Taurohyodeoxycholic acid was orally administered at dose levels up to 500 mg/kg/d and i.m. administered at dose levels up to 200 mg/kg/d. No deviations from normality were observed in mortality, physical appearance and general behaviour of the treated animals. Food and water consumption and body weight gain of treated groups did not differ from those of control animals. No treatment-related changes were observed in hematology, serum biochemistry, urinalysis, organ weights and post-mortem macroscopic or histopathological examinations. No dose- or sex-related differences were observed. The no-effect dose level was estimated to be 500 mg/kg/d in the chronic oral toxicity study and 200 mg/kg/d in the intramuscular study.

In vitro and in vivo mutagenicity studies on taurohyodeoxycholic acid

The mutagenicity of a new biliary acid, taurohyodeoxycholic acid (THDCA, Io, Praxis, CAS 2958-04-5), was assayed by using 5 different tests. The Ames test (reverse mutation assay on Salmonella typhimurium) and the DNA damage and repair test (in Saccharomyces cerevisiae) allowed to study the genetic THDCA-induced mutations in prokaryotes and eukaryotes (doses of 100, 200 and 400 micrograms/plate or 100, 200 and 400 micrograms/ml, respectively). In vivo and in vitro chromosomal aberrations were studied by using micronucleus test in mice (doses of 100, 220 and 500 mg/kg in oral study and 50, 100 and 200 mg/kg in subcutaneous study) and human lymphocytes cytogenetic test (doses of 50, 100, 220 and 500 micrograms/ml of THDCA). At last the host-mediated assay was performed on THDCA-treated mice (following oral or subcutaneous administration) in order to test the potential mutagenic activity of its metabolites on a S. typhimurium strain. The results obtained in these studies showed that THDCA did not induce any signs of promutagenic, mutagenic or clastogenic direct or metabolite-mediated activity.

Prophylactic octreotide reduces the severity of histopathologic changes and hemodynamic shock in early taurodeoxycholate-induced experimental pancreatitis

The findings related to the effects of somatostain and octreotide in experimental and clinical acute pancreatitis are so far inconclusive. In this study, we examined the early effects of prophylactic octreotide in acute experimental pancreatitis. Serum levels of amylase and lipase, pancreatic histopathology and systemic hemodynamic profiles, including mean arterial pressure, cardiac index, systemic vascular resistance and heart rate, were evaluated 5 hours after glycodeoxycholic acid (GDOC) or sodium taurodeoxycholate (TDC)-induced pancreatitis with or without prophylactic octreotide (10 micrograms/Kg) in rats, GDOC and TDC induced mild and severe pancreatitis, respectively. Octreotide significantly reduced serum levels of amylase and lipase at 5 hours in GDOC and TDC-induced pancreatitis. Octreotide significantly reduced the severity of pancreatic edema, necrosis and hemorrhage in TDC-induced pancreatitis. In addition, hemodynamic shock in TDC-induced pancreatitis was improved significantly by the administration of octreotide (mean arterial pressure 70.3 +/- 7.7 vs. 95.0 +/- 3.5 mmHg, p < 0.05; cardiac index 16.7 +/- 2.5 vs. 24.0 +/- 5.1 ml.min-1. 100 g-1, p < 0.05). However, octreotide did not show significant beneficial effect in pancreatic histopathology and hemodynamics in GDOC-induced pancreatitis. Thus we conclude that prophylactic octreotide improves pancreatic histopathology and hemodynamic shock in TDC-induced pancreatitis.