Unconjugated Ursodeoxycholic Acid Research Articles

Sex-, age-, and organ-dependent improvement of bile acid hydrophobicity by ursodeoxycholic acid treatment: A study using a mouse model with human-like bile acid composition.

Cyp2a12-/-Cyp2c70-/- double knockout (DKO) mice have a human-like hydrophobic bile acid (BA) composition and show reduced fertility and liver injury. Ursodeoxycholic acid (UDCA) is a hydrophilic and cytoprotective BA used to treat various liver injuries in humans. This study investigated the effects of orally administered UDCA on fertility and liver injury in DKO mice. UDCA treatment prevented abnormal delivery (miscarriage and preterm birth) in pregnant DKO mice, presumably by increasing the hydrophilicity of serum BAs. UDCA also prevented liver damage in six-week-old DKO mice, however liver injury emerged in UDCA-treated 20-week-old female, but not male, DKO mice. In 20-week-old male UDCA-treated DKO mice, conjugated plus unconjugated UDCA proportions in serum, liver, and bile were 71, 64, and 71% of the total BAs, respectively. In contrast, conjugated plus unconjugated UDCA proportions in serum, liver, and bile of females were 56, 34, and 58% of the total BAs, respectively. The UDCA proportion was considerably low in female liver only and was compensated by highly hydrophobic lithocholic acid (LCA). Therefore, UDCA treatment markedly reduced the BA hydrophobicity index in the male liver but not in females. This appears to be why UDCA treatment causes liver injury in 20-week-old female mice. To explore the cause of LCA accumulation in the female liver, we evaluated the hepatic activity of CYP3A11 and SULT2A1, which metabolize LCAs to more hydrophilic BAs. However, there was no evidence to suggest that either enzyme activity was lower in females than in males. As female mice have a larger BA pool than males, excessive loading of LCAs on the hepatic bile salt export pump (BSEP) may be the reason for the hepatic accumulation of LCAs in female DKO mice with prolonged UDCA treatment. Our results suggest that the improvement of BA hydrophobicity in DKO mice by UDCA administration is sex-, age-, and organ-dependent.

Small bowel obstruction due to an unconjugated ursodeoxycholic acid enterolith following living donor liver transplantation: Report of a case.

We report an unusual case of small bowel obstruction due to an ursodeoxycholic acid (UDCA) enterolith that occurred 7 years after liver transplantation. A 70-year-old man had undergone multiple operations, including a living donor liver transplantation (LDLT) and hepaticojejunostomy. Four years after the LDLT, cholestasis developed, for which oral UDCA was administrated. Seven years after the LDLT, he was admitted to our hospital because of pneumonia; intestinal obstruction occurred following its resolution. A radiographic contrast study and computed tomographic scan indicated a movable mass as the cause of the ileus, suggesting a giant stone. We were unable to observe or remove the stone by double balloon enteroscopy owing to the presence of severe adhesion; thus, we surgically removed the mass. The patient's postoperative course was uneventful. He was discharged 20 days after the operation. An infrared spectrophotometric analysis revealed that the stone was a true enterolith, primarily composed of unconjugated UDCA. An ileus caused by a true enterolith is a rare clinical complication of LDLT. Nevertheless, it must be considered in the differential diagnosis of intestinal obstructions in liver transplant recipients with Roux-en-Y hepaticojejunostomies and/or bowel stasis.

A monoclonal antibody-based enzyme-linked immunosorbent assay of ursodeoxycholic acid 3-sulfates in human urine

Sulfation of the 3-hydroxy group is assumed to be a major metabolic route of ursodeoxycholic acid (UDCA) which is used for treating various hepatobiliary diseases. We have developed a sensitive enzyme-linked immunosorbent assay (ELISA) for determining the total amount of nonamidated, glycine- and taurine-amidated ursodeoxycholic acid 3-sulfates (UDCA 3-Suls) using a newly established monoclonal antibody. In this study, 12 kinds of antibody-secreting hybridoma clones were generated by a fusion experiment between P3/NS1/1-Ag4-1 myeloma cells and the spleen cells from a BALB/c or an A/J mouse which had been immunized with a conjugate of nonamidated UDCA 3-Sul and bovine serum albumin. One of the monoclonal antibodies, Ba-10 (γ2a, κ), had suitable binding properties for clinical application, which was group-specific to the UDCA 3-Suls, and showed negligible cross-reactivities with various related bile acids including potentially interfering compounds, namely, the unconjugated UDCA, UDCA 7- N-acetylglucosaminide, the 3-sulfates of cholic acid, chenodeoxycholic acid and deoxycholic acid. The antibody Ba-10 allowed us to develop a sensitive competitive ELISA system whose measurable range was approximately 2–200 pg per assay. A serial dilution study indicated that the ELISA enables the direct measurement of the UDCA 3-Suls in human urine before and after the administration of exogenous UDCA. The daily urinary excretion rate of UDCA 3-Suls from healthy male volunteers ( n = 5) was determined to be a mean of 131 ± 61.2 (SD) μg as the nonamidated UDCA 3-Sul equivalent.

Effect of cholestyramine on bile acid pattern and synthesis during administration of ursodeoxycholic acid in man.

Cholestyramine is the first-line treatment for cholestasis-induced pruritus and is prescribed along with ursodeoxycholic acid (UDCA) in patients with cholestatic liver diseases. Impairment of the intestinal absorption of endogenous hydrophobic bile acids by cholestyramine is well known. It is unclear, however, whether cholestyramine also impairs the absorption of the hydrophilic bile acid, UDCA, in man. To study serum levels of UDCA and endogenous bile acids as well as endogenous bile acid synthesis during simultaneous or separate administration of UDCA and cholestyramine in vivo; and absorption of UDCA both in the presence and absence of its hydrophobic epimer, chenodeoxycholic acid (CDCA), by cholestyramine in vitro. Five healthy subjects received UDCA (12.5 +/- 0.5 mg kg-1 daily) as a single dose for periods of 14 days with or without cholestyramine (4 g daily). Fasting serum levels of bile acids and of 7alpha-hydroxy-4-cholesten-3-one (alpha-HC), a measure of endogenous bile acid synthesis, were determined by gas chromatography and high pressure liquid chromatography, respectively. In vitro, bile acid solutions were incubated for 24 h in the presence or absence of cholestyramine, and bile acid concentrations were determined in the supernatant. Simultaneous administration of UDCA and cholestyramine in man led to a decrease of fasting serum levels of UDCA by 60% when compared to UDCA serum levels during administration of UDCA alone. In contrast, serum levels of endogenous bile acids were not affected and alpha-HC serum levels were found increased 2. 7-fold indicating stimulation of endogenous bile acid synthesis by cholestyramine. Administration of cholestyramine and UDCA at an interval of 5 h tended to diminish the effect of cholestyramine on UDCA serum levels. In vitro, conjugated and unconjugated UDCA were effectively bound by cholestyramine both in the presence and absence of hydrophobic bile acids. The results strongly support the recommendation to administer UDCA and cholestyramine at different times of day.

Effect of cholestyramine on bile acid pattern and synthesis during administration of ursodeoxycholic acid in man

Background Cholestyramine is the first-line treatment for cholestasis-induced pruritus and is prescribed along with ursodeoxycholic acid (UDCA) in patients with cholestatic liver diseases. Impairment of the intestinal absorption of endogenous hydrophobic bile acids by cholestyramine is well known. It is unclear, however, whether cholestyramine also impairs the absorption of the hydrophilic bile acid, UDCA, in man. Aims To study serum levels of UDCA and endogenous bile acids as well as endogenous bile acid synthesis during simultaneous or separate administration of UDCA and cholestyramine in vivo; and absorption of UDCA both in the presence and absence of its hydrophobic epimer, chenodeoxycholic acid (CDCA), by cholestyramine in vitro. Patients and methods Five healthy subjects received UDCA (12.5 ± 0.5 mg kg−1 daily) as a single dose for periods of 14 days with or without cholestyramine (4 g daily). Fasting serum levels of bile acids and of 7α-hydroxy-4-cholesten-3-one (α-HC), a measure of endogenous bile acid synthesis, were determined by gas chromatography and high pressure liquid chromatography, respectively. In vitro, bile acid solutions were incubated for 24 h in the presence or absence of cholestyramine, and bile acid concentrations were determined in the supernatant. Results Simultaneous administration of UDCA and cholestyramine in man led to a decrease of fasting serum levels of UDCA by 60% when compared to UDCA serum levels during administration of UDCA alone. In contrast, serum levels of endogenous bile acids were not affected and α-HC serum levels were found increased 2.7-fold indicating stimulation of endogenous bile acid synthesis by cholestyramine. Administration of cholestyramine and UDCA at an interval of 5 h tended to diminish the effect of cholestyramine on UDCA serum levels. In vitro, conjugated and unconjugated UDCA were effectively bound by cholestyramine both in the presence and absence of hydrophobic bile acids. Conclusions The results strongly support the recommendation to administer UDCA and cholestyramine at different times of day.

Bile acid conjugation in early stage cholestatic liver disease before and during treatment with ursodeoxycholic acid

The efficiency of bile acid conjugation before and during therapy with 600 mg/day of ursodeoxycholic acid was measured in seven adult patients with early chronic cholestatic liver disease (6 with primary biliary cirrhosis; 1 with primary sclerosing cholangitis). Duodenal bile samples were obtained by aspiration and the proportion of unconjugated bile acids was determined using lipophilic anion exchange chromatography to separate bile acid classes, followed by analysis of individual bile acids by gas chromatography-mass spectrometry. The proportion of conjugated bile acids was determined by high-performance liquid chromatography. Use of a 99mTc-HIDA recovery marker permitted the absolute mass of unconjugated bile acids in the gallbladder to be calculated. Unconjugated bile acids comprised 0.4% of total biliary bile acids before and 0.2% during ursodeoxycholic acid therapy, indicating highly efficient conjugation of bile acids. During therapy, percentage unconjugated ursodeoxycholic acid significantly increased from (mean ± S.D.) 13 ± 13% to 54 ± 12%; P < 0.002. When the unconjugated and conjugated fractions of bile acids were compared, there was an enrichment in unconjugated fraction for cholic acid and ursodeoxycholic acid and a depletion for chenodeoxycholic acid both in basal condition and during ursodeoxycholic acid therapy, suggesting that hydrophilic bile acids were conjugated less efficiently. During therapy, the conjugation efficiency significantly increased for cholic acid and ursodeoxycholic acid. The pretreatment mass of total unconjugated bile acids in the gallbladder was (mean ± S.D.) 4.4 ± 3.2 μmol, and was not significantly changed by ursodeoxycholic acid therapy (6.2 ± 3.5 μmol). However, ursodeoxycholic acid therapy caused a significant increase in the mass of unconjugated ursodeoxycholic acid. It is concluded that endogenous bile acids and exogenous ursodeoxycholic acid when given at the usual dose are efficiently conjugated in patients with early cholestatic liver disease. Despite showing increased biliary unconjugated ursodeoxcholic acid during its oral administration, our data do not lend support to the occurrence of hypercholeresis due to cholehepatic shunting of bile acids.

Tauroursodeoxycholic acid protects in vitro models of human colonic cancer cells from cytotoxic effects of hydrophobic bile acids

Bile acids have been implicated as tumor promoters that enhance epithelial proliferation and the development of colonic tumors. This study investigated the effects of bile acids on the growth of in vitro models of human colonic epithelial cells. Cell lines with varying degrees of differentiation (Caco2, HT29, LS174T, and Lovo) were studied. Cell viability and number were measured by a tetrazolium (MTT) spectrophotometric assay. Enhanced cell growth was not observed with any bile acid over the range 10 nmol/L to 2.5 mmol/L. Cytotoxicity was consistently observed at concentrations of unconjugated bile acids greater than 0.1 mmol/L. The bile acid concentration at which 50% growth inhibition occurred was similar for all cell lines and increased in the following order: deoxycholic acid = chenodeoxycholic acid < taurodeoxycholic acid < ursodeoxycholic acid < taurochenodeoxycholic acid < cholic acid < tauroursodeoxycholic acid. Coincubation of tauroursodeoxycholic acid (TUDC) with taurodeoxycholic acid (TDC) or taurochenodeoxycholic acid (TDCD) reversed the short-term (30-minute) cytotoxicity and release of glycoprotein induced by TDC or TCDC regardless of differentiation status. In contrast, TUDC did not reverse the cytotoxicity of deoxycholic acid. Unconjugated ursodeoxycholic acid did not alter short-term cytotoxicity of any bile acid. These data indicate that bile acids do not stimulate cell growth in undifferentiated or differentiated colon cancer cell lines, in contrast to normal colonic epithelium in vivo. Bile acid cytotoxicity correlates with the relative hydrophobicity of the bile acid. Because tauroursodeoxycholic acid alters the cytotoxicity of hydrophobic bile acids in vitro, further understanding of bile acid interactions in the colon may have important implications in altering tumor promotion.

Effect of ursodeoxycholic acid on intracellular pH in a bile duct epithelium-like cell line

Recent studies in perfused livers and isolated hepatocytes indicate that ursodeoxycholic acid-induced HCO3-rich hypercholeresis originates at the ductule/duct level. The bile duct epithelium may be involved in bile alkalinization by passively reabsorbing the protonated unconjugated ursodeoxycholic acid, by directly secreting in response to an ursodeoxycholic acid-induced increase in acid/base transporter activity or by taking up UDCA- in exchange for a base equivalent. To investigate these processes in more detail, we studied the effects of ursodeoxycholic acid on intracellular pH in SK-ChA-1, a well-differentiated human cholangiocarcinoma cell line similar to bile duct epithelium in terms of intracellular pH regulatory mechanisms and morphological markers. Intracellular pH changes were monitored with a microfluorimetric setup using the fluorescent indicator 2'-7'-bis(2-carboxyethyl)-5,6,carboxy fluorescein. Administration of 50 to 1,000 mumol/L UDCA in the absence of HCO3 caused dose-dependent intracellular acidification (intracellular pH = -0.13 +/- 0.03 pH/U after 500 mumol/L ursodeoxycholic acid). Acidification was not prevented by preincubation of cells with 0.5 mmol/L 4,4-diisothiocyanatostilbene-2,2,-disulfonic acid (DIDS) for 30 min or by furosemide administration (1 mmol/L), thus ruling out the stimulation of Cl/HCO3 exchange or the presence of an ursodeoxycholic acid/base exchange. Ursodeoxycholic acid also acidified human fibroblasts, a cell type with no transport capability for ursodeoxycholic acid. In addition, direct measurement of the activities of the three major acid/base transporters in Sk-ChA-1 cells (Na+/H+ exchange, sodium-dependent and sodium-independent Cl/HCO3 exchange) failed to show significative differences between cells treated with 500 mumol/L UDCA and controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of selective zonal injury on bile acid-induced bile flow in the isolated rat liver.

The importance of acinar heterogeneity in ursodeoxycholic acid (UDCA)-induced bile flow was assessed in isolated rat livers that underwent restricted acinar damage by antegrade (A; 50 nmol) or retrograde (R; 500 nmol) digitonin infusion, as confirmed by histological evaluation. Stability of reduced (-40%) bile flow and perfusion flow (-25%) at constant pressure and potassium and lactate dehydrogenase release indicated similar viability of A and R preparations. They also showed similar abilities to secrete increasing doses of taurocholate (TC, maximal secretion rate approximately 105 nmol.min-1.g liver-1). TC-induced bile flow was not reduced by digitonin. In contrast, UDCA-induced choleresis was sensitive to zonal injury. Moreover, increases in bile flow and bicarbonate secretion observed under UDCA infusion (1.5 mumol/min) were lower in R than in A (-33 and -51%, respectively). No significant difference was observed in UDCA amidation or glucuronation between A and R preparations. With the use of single-pass perfusion on intact isolated livers that received 1 or 10 mumol UDCA, an early peak in bile acid output was observed to occur before the appearance of the major secretory peak. This was not found when 1 mumol of chenodeoxycholic acid bolus or trace amounts of [14C]TC were given. High-performance liquid chromatographic analysis of the early peak revealed it to be mainly due to unconjugated UDCA. This suggests the existence of a diffusional pathway for protonated bile acids and hence that the exist of lipophilic UDCA from bile during its way through the intra-acinar canaliculi across this pathway is also possible.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in bile acid composition in patients with primary biliary cirrhosis induced by ursodeoxycholic acid administration

We describe a detailed study of the effects of ursodeoxycholic acid administration on bile acid composition of the serum and bile of patients with primary biliary cirrhosis. Gas chromatography-mass spectrometry was used to analyze bile acids from 10 patients with primary biliary cirrhosis before and during ursodeoxycholic acid administration (500 mg/day, corresponding to approximately 8 mg/kg body wt), after group separation of the unconjugated and conjugated fractions by lipophilic anion exchange chromatography. These studies were directed at assessing whether the beneficial role of ursodeoxycholic acid in primary biliary cirrhosis was the consequence of a shift in the hydrophobic/hydrophilic balance of the bile acid pool and whether the hypercholeresis might result from the cholehepatic circulation of unconjugated ursodeoxycholic acid in bile. In basal conditions, the unconjugated bile acids accounted for only 5.5% and 2.5%, respectively, of the total bile acids of serum and bile; cholic acid was the major component of the conjugated fraction of serum and bile (56.0% ± 4.0%, mean ± S.E.M.), and ursodeoxycholic acid was present in only trace amounts. The conjugated fraction contained many unusual bile acids (representing 16.5% ± 1.3% of total) including C 25 bile acids, iso-chenodeoxycholic acid and several oxo-bile acids. After ursodeoxycholic acid administration biochemical indices of liver function all improved, but the proportions of the unconjugated bile acids in serum and bile did not significantly change. Ursodeoxycholic acid became the predominant biliary bile acid of conjugated bile acid fraction (33.4% ± 1.4%) and significant decreases occurred (p < 0.05) in biliary levels of cholic acid (28.3% ± 2.3%) and the unusual bile acids (9.2% ± 0.8%), but no changes occurred in the proportions of chenodeoxycholic acid (from 19.4% ± 2.7% to 19.4% ± 1.3%) and deoxycholic acid (from 5.4% ± 1.4% to 6.8% ± 1.3%). The proportions of biliary lithocholic acid increased significantly after ursodeoxycholic acid administration (from 0.7% ± 0.1% to 2.9% ± 0.9%; p < 0.05). In serum, ursodeoxycholic acid concentrations attained levels of 64 μmol/L. Serum lithocholic acid concentrations increased, whereas cholic and chenodeoxycholic acids decreased. Relative percentages of individual biliary bile acids in the unconjugated fraction were similar to the conjugated fraction before and after ursodeoxycholic acid treatment. The proportions of biliary unconjugated ursodeoxycholic acid did not change significantly after its administration (from 0.6% to 0.9% of the total). These data provide little support for a significant shift in the hydrophilicity of the circulating bile acid pool after ursodeoxycholic acid administration. However, because the detergency and hepatotoxicity of a bile salt appears to correlate well with the retention index determined by reverse-phase liquid chromatography, the qualitative changes observed in the biliary pool (i.e., a displacement of cholic acid by ursodeoxycholic acid), suggests that a relative lowering of the hepatotoxicity index of the bile acid pool occurs after ursodeoxycholic acid therapy. Furthermore, our findings indirectly suggest that a hypercholeresis related to the biliary secretion of unconjugated ursodeoxycholic acid does not play a role in the beneficial effects of ursodeoxycholic acid therapy in primary biliary cirrhosis.

Changes in bile acid composition in patients with primary biliary cirrhosis induced by ursodeoxycholic acid administration

We describe a detailed study of the effects of ursodeoxycholic acid administration on bile acid composition of the serum and bile of patients with primary biliary cirrhosis. Gas chromatography-mass spectrometry was used to analyze bile acids from 10 patients with primary biliary cirrhosis before and during ursodeoxycholic acid administration (500 mg/day, corresponding to approximately 8 mg/kg body wt), after group separation of the unconjugated and conjugated fractions by lipophilic anion exchange chromatography. These studies were directed at assessing whether the beneficial role of ursodeoxycholic acid in primary biliary cirrhosis was the consequence of a shift in the hydrophobic/hydrophilic balance of the bile acid pool and whether the hypercholeresis might result from the cholehepatic circulation of unconjugated ursodeoxycholic acid in bile. In basal conditions, the unconjugated bile acids accounted for only 5.5% and 2.5%, respectively, of the total bile acids of serum and bile; cholic acid was the major component of the conjugated fraction of serum and bile (56.0% +/- 4.0%, mean +/- S.E.M.), and ursodeoxycholic acid was present in only trace amounts. The conjugated fraction contained many unusual bile acids (representing 16.5% +/- 1.3% of total) including C25 bile acids, iso-chenodeoxycholic acid and several oxo-bile acids. After ursodeoxycholic acid administration biochemical indices of liver function all improved, but the proportions of the unconjugated bile acids in serum and bile did not significantly change.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatocellular bile acid transport and ursodeoxycholic acid hypercholeresis.

This review focuses on mechanisms of bile acid transport across the basolateral and canalicular hepatocyte plasma membranes and on ursodeoxycholic acid (UDCA) hypercholeresis and biotransformation. Conjugated trihydroxy bile acids enter hepatocytes via a sodium-coupled mechanism localized to the basolateral membrane, which is saturable, concentrative, inhibited by other bile acids as well as by furosemide and bumetanide, and exhibits developmental changes in rats and probably also in humans. The stoichiometry of sodium-coupled bile acid uptake has been controversial. Hydrophobic, unconjugated dihydroxy and monohydroxy bile acids, including UDCA, enter hepatocytes more rapidly than does taurocholate, and their uptake is largely nonsaturable and sodium independent. A hydroxyl-exchange mechanism that mediates the uptake of cholic acid has also been reported, but its existence is controversial. Current evidence suggests that a 49-kDa protein mediates Na+-dependent taurocholate uptake and that a 54-kDa protein is involved in Na+-independent bile acid uptake. Studies with canalicular membrane vesicles have demonstrated saturable, sodium-independent taurocholate transport, which is sensitive to electrical potential, exhibits trans-stimulation, and appears to be mediated by a 100-kDa canalicular membrane glycoprotein. Studies in mutant rats with conjugated hyperbilirubinemia suggest the presence of a separate canalicular transport mechanism utilized by sulfated bile acids and organic anions such as bilirubin and sulfobromophthalein. UDCA produces in some species a dramatic hypercholeresis that is greater than expected based on the osmotic effect of the secreted bile acid. The hypercholeresis appears attributable to stimulation of biliary bicarbonate output and is decreased or abolished in the perfused rat liver by amiloride or perfusate Na+ substitution. These same maneuvers dramatically alter UDCA biotransformation (unconjugated UDCA disappears from bile, and UDCA glucuronide becomes a major metabolite) and lower hepatocyte intracellular pH. These and other findings indicate that UDCA hypercholeresis is tightly linked to biliary excretion of the unconjugated species and suggest that UDCA biotransformation may be influenced by intracellular pH.

Serum Concentrations of Ursodeoxycholic Acid in Portal Venous and Systemic Venous Blood of Fasting Humans as Determined by Isotope Dilution—Mass Spectrometry

The fasting concentrations of ursodeoxycholic acid were determined in peripheral and portal venous serum of untreated (n = 12) and ursodeoxycholic acid-treated (n = 7) patients undergoing cholecystectomy. The levels of ursodeoxycholic acid were also determined in peripheral venous serum of 9 healthy subjects before and during treatment with ursodeoxycholic acid. Ursodeoxycholic acid, as well as cholic, chenodeoxycholic, and deoxycholic acids, were analyzed by a highly specific method based on isotope dilution-mass spectrometry. The fasting peripheral venous serum concentration of total (unconjugated plus conjugated) ursodeoxycholic acid averaged 0.14 mumol/L in the untreated gallstone patients and 0.19 mumol/L in the healthy subjects. The corresponding value in portal venous serum was 0.44 mumol/L. Treatment with ursodeoxycholic acid raised the level of this bile acid about 25-fold in portal as well as in peripheral venous serum. The proportion of unconjugated ursodeoxycholic acid was 34% in portal and 49% in peripheral venous serum of treated subjects. The mean hepatic uptake of ursodeoxycholic acid was calculated to be about 60% both in untreated and treated subjects. This uptake was significantly lower than that of cholic acid (83%). The hepatic uptake of ursodeoxycholic acid also tended to be lower than that of chenodeoxycholic acid (68%). This was mainly due to a lower hepatic uptake of unconjugated ursodeoxycholic acid (34%) compared with unconjugated chenodeoxycholic acid (49%). The relatively low hepatic uptake of unconjugated ursodeoxycholic acid explains why serum levels of the administered bile acid are higher during treatment with ursodeoxycholic acid than during treatment with chenodeoxycholic acid. Our results also give evidence that the hepatic uptake of ursodeoxycholic acid cannot be saturated under physiologic conditions.

Portal‐systemic spill‐over of bile acids: a study of mechanisms using ursodeoxycholic acid

Portal-systemic spill-over of unconjugated ursodeoxycholic acid (UDCA) was assessed in ten healthy subjects, six patients with mild chronic liver disease and eight patients with cirrhosis. Following oral administration of UDCA (1.5 mg/kg body weight), serum concentrations of unconjugated UDCA were measured during 2 h using a capillary gas-liquid chromatographic method. Peak time of UDCA varied from 15 to 30 min, but was not significantly different in the three groups studied. Peak concentration was increased up to two-fold in patients with mild, and up to three-fold in patients with cirrhotic liver disease. Since, in addition, plasma disappearance rate (k) was markedly impaired in cirrhotics (1.7 +/- SD 0.5%/min, compared to 2.8 +/- 0.6 in healthy controls), the calculated area under the curve (AUC) was on the average five-fold that in controls. In two healthy and four cirrhotic subjects, the data obtained after oral administration were compared with those after i.v. loading with the same UDCA dose. The k-values after the two routes of administration were practically identical. Calculated systemic availability was 50% in normals, 78-87% in cirrhotics, 90 and 136% in two patients with surgical porta-caval shunt. It is concluded that the portal-systemic spill-over of UDCA in patients with liver disease is increased primarily due to portal-systemic shunting. Since in the normal liver hepatic extraction of conjugated, endogenous bile acids is greater than 80%, diminished first-pass elimination is expected to augment systemic concentrations even more, particularly when measured after a meal.

Enrichment of bile with tauroursodeoxycholic acid and biliary cholesterol saturation in hamsters

Three groups of golden Syrian hamsters were fed equimolar amounts of taurine-conjugated ursodeoxycholic acid (TUDCA) or unconjugated ursodeoxycholic acid (UDCA) with or without excess taurine for 2 wk. They also received a lithogenic diet composed of standard rodent chow containing ethynylestradiol and increased cholesterol. Bile was obtained from the gallbladder after ketamine anesthesia and analyzed for biliary lipids. The percentage of biliary UDCA was higher with TUDCA (38.5 +/- 3.7) than with UDCA plus taurine (26.5 +/- 2.0, P less than 0.01). The glycine-to-taurine ratio of biliary UDCA conjugates was lower with TUDCA (0.9 +/- 0.1) than with UDCA plus taurine (2.1 +/- 0.2, P less than 0.01) and was highest with UDCA without taurine (4.1 +/- 0.1, P less than 0.01). Biliary cholesterol (molar percentage) and the cholesterol saturation indices with or without correction for UDCA-rich bile were significantly lower with TUDCA than with unconjugated UDCA with or without added taurine. In conclusion, administration for 2 wk of TUDCA, compared with an equimolar amount of unconjugated UDCA plus taurine, produced in the bile of hamsters a higher percentage of UDCA, a lower glycine-to-taurine ratio of UDCA conjugates, and a lower saturation index before and after adjustment for UDCA-rich bile.