Mesophase formation during cholesterol gallstone dissolution in human bile: effect of bile acid composition

Duodenal bile obtained from patients with gallstones who were acutely infused with chenodeoxycholic acid, ursodeoxycholic acid, or cholic acid were examined for the propensity toward the formation of a liquid crystalline mesomorphic phase when cholesterol gallstones were incubated in these bile acids. Bile taken from patients infused with ursodeoxycholic acid was found to be enriched in ursodeoxycholic acid; mesophase formation was detected in these samples but not in bile from patients infused with chenodeoxycholic acid or cholic acid.     

Comparison of the choleretic properties of bile acids

The choleretic properties of cholic, chenodeoxycholic, and deoxycholic acid and their taurine and glycine conjugates were compared to their ability to form micelles. It has previously been concluded that deoxycholate has the lowest critical micellar concentration; chenodeoxycholate is slightly higher and cholic is much higher. Conjugation with glycine and taurine has little or no effect on the critical micelle concentration. Since the choleretic properties of bile salts are thought to be directly proportional to their osmotic activities, one might suspect that deoxycholic acid would be the least choleretic, chenodeoxycholic slightly more choleretic and cholic much more choleretic, with little difference between the conjugated and unconjugated forms. However, in the present study, cholic, chenodeoxycholic and taurocholic acid produced similar increases in bile flow (450–700 μl/kg) after an equimolar dose (55 μM/kg). Except for the conjugation of deoxycholic acid with taurine, conjugation of these bile acids with glycine or taurine always decreased the choleretic properties of the bile acids. Therefore, it has been concluded that there is not a good correlation between the in vitro osmotic properties of bile acids and their ability to increase bile flow.     

Correlation of biliary cholesterol, phospholipids and bile acid compositions and the development of cholesterol cholelithiasis in mice

A study was attempted to establish a screening method for detecting cholelitholytic ingredients from a wide variety of natural substances. Although mice were selected as a suitable pathological model of cholelithiasis to detect a small amount of the ingredients, all the conventional lithogenic diets caused unfavorable influence on the animals. Therefore, as the first step we formulated a new lithogenic diet consisting of butter, cholesterol, cholic acid, etc, which was adequate for mice. Subsequently, the pathological characteristics and persistence of cholelithiasis were examined in the animals; the changes in bile compositions including free and conjugated bile acids, cholesterol and phospholipids were observed before and at the onset of cholelithiasis. Following confirmation of the stone formation, a normal diet was substituted for the lithogenic diet to likewise assess the bile compositions 4 and 6 weeks later. An increasing tendency for deoxycholic acid, disappearance of chenodeoxycholic acid and decrease in ursodeoxycholic acid were seen under the condition of cholelithiasis. In addition, the cholic acid-glycine conjugate which should not exist in the normal state and the increase in free and tauring-conjugated cholic acid were noticed. The biliary cholesterol level in treated mice increased to about 4 times higher than that in untreated mice, while the biliary phospholipids and total bile acids levels increased to only about 1.5 and about 2 times the control levels, respectively. The incidence of stone formation rose sharply at an experimental period between 2 and 3 weeks after starting the lithogenic diet. Gallstones die not disappear even at the 6th week after substituting a normal diet for the lithogenic one. However, the cholic acid-glycine conjugate disappeared, and deoxycholic acid as well as chenodeoxycholic acid and ursodeoxycholic acid tended to recover to the normal levels in the bile.     

Altered bile acid metabolism in alloxan diabetic rats

Changes of cholesterol, phospholipid, triglyceride or bile acid levels in serum liver, bile and feces after the treatment with alloxan were examined in Wistar strain male rats. Serum cholesterol, phospholipid and triglyceride levels and liver cholesterol level markedly increased but liver phospholipid and triglyceride levels remained unchanged. The lipid levels in serum very low density and low density lipoproteins were elevated but those in high density lipoprotein were not. Bile flow was not changed but biliary secretion of cholesterol, phospholipid and bile acids markedly increased. Among the biliary bile acid components, cholic acid markedly increased but the amount of chenodeoxycholic acid was similar to that of normal rats. Fecal excretion of deoxycholic acid increased but that of lithocholic and hyodeoxycholic acids decreased, and alpha, beta- and omega-muricholic acids did not change, thus, the total amount of fecal bile acids remained unchanged. Hepatic cholesterol synthesis was markedly depressed, while cholesterol 7 alpha-hydroxylase activity did not change and cytochrome P-450 content was elevated by about 40%. From such evidence, it was apparent that synthesis of cholic acid increased while that of chenodeoxycholic acid decreased and the total amount of bile acids synthesized did not change in the diabetic rats. Furthermore, marked increase of the pool size of cholic acid and hepatic secretion of cholic acid stimulated the absorption of lipids and produced a hyperlipidemia in the diabetic rats.     

Bile acids in porcine fetal bile

A study of the biliary bile acid composition in porcine fetus compared with that of the adult pig is described. Biles, collected during gestation (weeks 4, 15 to 17 and at birth), aged six months and two years old, were analyzed by gas-liquid chromatography and capillary GC-MS. Bile acids were separated into different conjugate groups by chromatography on the lipophilic anion exchange gel, piperidinohydroxypropyl Sephadex LH-20. All and one fourth of the total bile acids in the bile of weeks 4 and 15 of gestation, respectively, were present as unconjugated form, however, only a trace of unconjugated bile acids was present in bile of late gestation, the young and the adult pigs. The ratio of glycine/taurine (G/T) conjugates in the conjugated fraction of the fetal bile at 15 weeks gestation was less than 1, which markedly contrasted with the conjugation pattern for adult bile where the ratio of G/T conjugates was approximately more than 9. The predominant acids identified in porcine fetal bile of the 4 weeks gestation were cholic acid (3alpha,7alpha,12alpha-trihydroxy-5beta-chola n-24-oic acid) and chenodeoxycholic acid (3alpha,7alpha -dihydroxy-5beta-cholan-24-oic acid). However, cholic acid in late gestation, young, and adult bile was the smallest component, whereas chenodeoxycholic acid was still the major constituent of these biles. The presence of small but valuable amounts of allocholic acid (3alpha,7alpha,12alpha-trihydroxy-5alpha-chol an-24-oic acid) and cholic acid in early gestation suggested the presence of 12alpha-hydroxylase activity of steroid nucleus in fetal liver. Considerable amounts of glycine-conjugated hyodeoxycholic acid were found in the bile of the gestation periods, suggesting the placental transfer of this bile acid from maternal circulation.     

The effect of drugs on bile flow and composition. An overview

Many drugs are eliminated via the hepatobiliary route, after biotransformation in the liver. Some of them may affect bile flow and/or the hepatic secretion of biliary lipids such as bile acids, cholesterol and phospholipids. Bile acids are the most potent agents which increase bile flow, especially unconjugated bile acids. Other drugs which increase bile flow include phenobarbitone (phenobarbital), theophylline, glucagon and insulin. In contrast, ethacrynic acid, amiloride, ouabain, oestrogens and chlorpromazine are among those agents which decrease bile flow. Biliary bile acid secretion is altered by a variety of drugs, including cheno- and ursodeoxycholic acids (CDCA and UCDA), the bile acid sequestrants cholestyramine and colestipol, and ethinyloestradiol. The composition of bile can also be altered by drug therapy. Thus, clofibrate increases biliary cholesterol secretion, and reduces bile acid concentrations, without altering biliary phospholipid concentrations. However, other clofibrate derivatives may produce changes of a different pattern, suggesting that the risk of developing gallstones may differ for each derivative. Nicotinic acid and d-thyroxine also increase biliary cholesterol saturation, while CDCA and UDCA reduce biliary cholesterol concentration. The potential consequences of drug-induced changes in bile flow and composition extend to the liver, the gallbladder and the intestine. If adverse effects are to be avoided, further study in this often overlooked area is required.     

Cholic acid and ursodeoxycholic acid therapy in primary biliary cirrhosis

Summary We treated 6 patients with Stage II primary biliary cirrhosis with cholic acid (CA) 10 mg · kg^–1 per day for 3 months and then with the same dose of ursodeoxycholic acid (UDCA). A matching group of 6 patients was observed for 3 months without any therapy. Liver function tests and serum and stool bile acids were investigated before, during and at the end of CA and UDCA therapy.The results of liver function tests deteriorated after 6–8 weeks of CA therapy and the changes were correlated (r=0.92) with an increase in -dihydroxy-bile acids (chenodeoxycholic acid and deoxycholic acid) in the serum. The 24 h excretion of DCA in 24 h faeces was markedly increased.Ursodeoxycholic acid treatment improved liver function tests; after 4 weeks glutamate dehydrogenase (GLDH) had decreased. After 8–12 weeks of therapy ursodeoxycholic acid had increased to 50–60% of the total serum bile acids whereas the more apolar bile acids were significantly decreased. No changes in liver function tests or bile acid metabolism were found in the untreated group.Since CA and UDCA are non-toxic in man, this trial indicates that the apolar bile acids chenodeoxycholic acid and deoxycholic acid may be responsible for the deterioration of liver function in primary biliary cirrhosis. However, the therapeutic effect of UDCA cannot be explained merely by the decrease in -dihydroxy-bile acids in the serum, since the laboratory results had improved prior to the decrease in the serum apolar bile acids.     

Ionization of unconjugated, glycine- and taurine-conjugated bile acids by electrospray ionization mass spectrometry

We investigated the effect of organic anions as spray liquid additives on the ionization efficiency of unconjugated, glycine-conjugated and taurine-conjugated bile acids under electrospray ionization conditions. Addition of organic acids influenced the ionization efficiency of whole bile acids. Use of a stronger acid reduced the peak intensity of unconjugated and glycine-conjugated bile acids, while the use of TFA, the strongest acid tested, improved the intensity of taurine conjugates. The hydroxyl group at the C-12 position of cholic acid and deoxycholic acid easily underwent intra-molecular hydrogen bonding with the side chain carboxyl group, accelerating the ionization efficiency. This intra-molecular hydrogen bond may also affect the formation of product ions in low energy-CID. The addition of ammonium ions to the spray liquid influenced the ionization of all bile acids, specifically enhancing the ionization efficiency of unconjugated bile acids.     

Inhibiting uptake activity of organic anion transporter 2 by bile acids

Bile acids, a series of amphiphilic molecules, can interact with several drug transporters and impact drug ADME. Organic anion transporter 2 (OAT2) is exclusively expressed in the liver and kidney. However, the interaction between bile acids and hOAT2 is unelucidated. In this study, we observed that chenodeoxycholic acid, deoxycholic acid, ursodeoxycholic acid, glycochenodeoxycholic acid (GCDCA), glycodeoxycholic acid, glycoursodeoxycholic acid (GUDCA), taurocholic acid (TCA), taurochenodeoxycholic acid (TCDCA), taurodeoxycholic acid, tauroursodeoxycholic acid could all inhibit uptake activity of hOAT2 while glycocholic acid (GCA) and cholic acid could not. Among them, TCDCA was the strongest inhibitor with IC₅₀ value of 23.01 ± 3.45 μM and GCDCA was the second with IC₅₀ value of 54.26 ± 5.47 μM. Meanwhile, GCA, GUDCA, TCA and TCDCA were identified as substrates of hOAT2. We further found that bile acid mixture (BA mix) could inhibit hOAT2-mediated uptake of cGMP, 5-fluorouracil, irinotecan and paclitaxel. BA mix could reduce the toxicity of paclitaxel to MDCK-hOAT2 cells. In addition, the uptake activity of three SNPs of hOAT2 (C329T, G571A, and G1514A) was all reduced. In conclusion, this study revealed bile acids could interact with hOAT2, providing new insight into the alteration of drug ADME and therapeutic effect mediated by hOAT2.     

Pharmacology of bile acids and their derivatives: absorption promoters and therapeutic agents.

The role of bile acids in pharmacotherapy is reviewed in this article. The therapeutic use of bile has been recognized since ancient times. Previously bile acids were the standard treatment for gallstones where chenodeoxycholic acid and ursodeoxycholic acid were effective in promoting the dissolution of cholesterol gallstones. Today their therapeutic role looks set to expand enormously. Bile acids as absorption promoters have the potential to aid intestinal, buccal, transdermal, ocular, nasal, rectal and pulmonary absorption of various drugs at concentrations that are non-toxic. Keto derivatives of cholic acid, such as 3a,7a,dihydroxy-12-keto-5alpha-cholic acid (sodium salt and methyl ester) are potential modifiers of blood-brain barrier transport and have been shown to promote quinine uptake, enhance the analgesic effect of morphine and prolong the sleeping time induced by pentobarbital. They have also been shown to be hypoglycaemic. Bile acids as therapeutic agents have the potential to produce beneficial effects in sexually transmitted diseases, primary biliary cirrhosis, primary sclerosing cholangitis, gallstones, digestive tract diseases, cystic fibrosis, cancer and diabetes.     

3alpha-6alpha-Dihydroxy-7alpha-fluoro-5beta-cholanoate (UPF-680), physicochemical and physiological properties of a new fluorinated bile acid that prevents 17alpha-ethynyl-estradiol-induced cholestasis in rats

3alpha-6alpha-Dihydroxy-7alpha-fluoro-5beta-cholanoate (UPF-680), the 7alpha-fluorine analog of hyodeoxycholic acid (HDCA), was synthesized to improve bioavailability and stability of ursodeoxycholic acid (UDCA). Acute rat biliary fistula and chronic cholestasis induced by 17alpha-ethynyl-estradiol (17EE) models were used to study and compare the effects of UPF-680 (dose range 0.6-6.0 micromol/kg min) with UDCA on bile flow, biliary bicarbonate (HCO(3)(-)), lipid output, biliary bile acid composition, hepatic enzymes and organic anion pumps. In acute infusion, UPF-680 increased bile flow in a dose-related manner, by up to 40.9%. Biliary HCO(3)(-) output was similarly increased. Changes were observed in phospholipid secretion only at the highest doses. Treatment with UDCA and UPF-680 reversed chronic cholestasis induced by 17EE; in this model, UDCA had no effect on bile flow in contrast to UPF-680, which significantly increased bile flow. With acute administration of UPF-680, the biliary bile acid pool became enriched with unconjugated and conjugated UPF-680 (71.7%) at the expense of endogenous cholic acid and muricholic isomers. With chronic administration of UPF-680 or UDCA, the main biliary bile acids were tauro conjugates, but modification of biliary bile acid pool was greater with UPF-680. UPF-680 increased the mRNA for cytochrome P450 7A1 (CYP7A1) and cytochrome P450 8B (CYP8B). Both UDCA and UPF-680 increased the mRNA for Na(+) taurocholate co-transporting polypeptide (NCTP). In conclusion, UPF-680 prevented 17EE-induced cholestasis and enriched the biliary bile acid pool with less detergent and cytotoxic bile acids. This novel fluorinated bile acid may have potential in the treatment of cholestatic liver disease.     

Differing effect of chenodeoxycholic acid and ursodeoxycholic acid on bile acids in rat colonic wall and contents

Bile acids may promote experimental colonic cancer. Many studies correlate fecal bile acids and colorectal carcinomas. Little is known on bile acids in the colonic mucosa and their relation to luminal bile acids. We, therefore, studied bile acids in colonic wall and contents of normal female Wistar rats and after 14 days' administration of chenodeoxycholic acid or ursodeoxycholic acid (90 mg/kg daily), two bile acids used in medicamentous cholelitholysis. Both regimens increase total bile acids in colonic contents, ursodeoxycholic acid produces a higher rise in toxic lithocholic acid. In the colonic wall, only ursodeoxycholic acid causes an increase of most nonsulfated bile acids including lithocholic acid. Bile acid patterns do not correlate in colonic wall and contents. We conclude that increased colonic wall bile acids after ursodeoxycholic acid administration warrant control in man. In future colorectal carcinoma studies, not only fecal, but also mucosal bile acid concentrations should be correlated to carcinogenesis.     

Inhibition of the rat hepatic microsomal flurbiprofen acyl glucuronidation by bile acids

Glucuronidation of carboxylic acids, primarily catalyzed by hepatic UDP-glucuronosyltransferases, is an important phase II metabolic pathway functioning in detoxification. Acyl glucuronides of 2-aryl propionates, however, can form covalently bound protein adducts, which may generate hypersensitive reactions. We previously identified and quantified R- and S-flurbiprofen acyl glucuronides in human urine following the oral administration of flurbiprofen by liquid chromatography/electrospray ionization mass spectrometry. Recent studies also demonstrated the inhibitory effect of bile acids and their metabolites toward rat hepatic bile acid acyl glucuronidation, which may also be the target of the flurbiprofen isoenzyme. We therefore performed a kinetic analysis of rat hepatic flurbiprofen UDP-glucuronosyltransferase using bisubstrate kinetic analysis and inhibition studies. The results indicated that both bile acid and its metabolites clearly inhibited flurbiprofen acyl glucuronidation. The inhibitory effect on flurbiprofen was more efficient than the effect seen on bile acid acyl glucuronidation. Unconjugated, glycine- and taurine-conjugated chenodeoxycholic acids inhibited glucuronidation using a noncompetitive mechanism, whereas the inhibition by chenodeoxycholic acid 24-acyl glucuronide occurred according to a mixed type mechanism. The inhibition by bile acids and their metabolites may be responsible for the suppression of the toxicity of carboxy-linked glucuronides.     

Ursodeoxycholic acid alone or with chenodeoxycholic acid for dissolution of cholesterol gallstones: a randomized multicentre trial. The British-Italian Gallstone Study group

BACKGROUND: Combination therapy using ursodeoxycholic acid plus chenodeoxycholic acid has been advocated for dissolution of cholesterol gallstones because the two bile acids have complementary effects on biliary lipid metabolism and cholesterol solubilization. AIM: To compare the clinical efficacy of combination therapy with ursodeoxycholic acid monotherapy. PATIENTS AND METHODS: A total of 154 symptomatic patients with radiolucent stones (< or = 15 mm) in functioning gallbladders were enrolled from six centres in England and Italy. They were randomized to either a combination of chenodeoxycholic acid plus ursodeoxycholic acid (5 mg.day/kg each) or to ursodeoxycholic acid alone (10 mg.day/kg). Dissolution was assessed by 6-monthly oral cholecystography and ultrasonography for up to 24 months. RESULTS: Both regimens reduced the frequency of biliary pain and there was no significant difference between them in terms of side-effects or dropout rate. Complete gallstone dissolution on an intention-to-treat basis was similar at all time intervals. At 24 months this was 28% with ursodeoxycholic acid alone and 30% with combination therapy. The mean dissolution rates at 6 and 12 months were 47% and 59% with ursodeoxycholic acid, and 44% and 59% with combination therapy, respectively. CONCLUSION: There is no substantial difference in the efficacy of combined ursodeoxycholic acid and chenodeoxycholic acid and that of ursodeoxycholic acid alone in terms of gallstone dissolution rate, complete gallstone dissolution, or relief of biliary pain.     

Mixed oxo-hydroxy bile acids as actual or potential impurities in ursodeoxycholic acid preparation: a 1H and 13C NMR study

Some distinctive unprecedented 1H NMR signals and the complete 13C NMR resonances are assigned for the entire set of mixed oxo-hydroxy bile acid isomers, obtained by selective oxidation of the hydroxy groups at positions (3,7), (3,12) and (3,7,12) of chenodesoxycholic acid, desoxycholic acid and cholic acid, respectively. Partially or totally oxidized products are the major actual or potential impurities formed during the preparation of the pharmaceutically active ursodeoxycholic and chenodeoxycholic acids.     

The influence of cholic acid and dehydrocholic acid on the biliary excretion of unconjugated and conjugated sulfobromophthalein in rats.

Urethane anesthetized Wistar rats with biliary fistulas were infused during 100 min with sulfobromophthalein (BSP), the glutathione conjugate of sulfobromophthalein (BSP-GSH), cholic acid (CA) and dehydrocholic acid (DCA). The dyes (594 nmol/100 g/min) and the bile acids (1200 nmol/100 g/min) were infused separately, and in combination as well. When BSP was infused, CA and DCA increased the maximal excretion of total BSP (conjugated plus unconjugated) from 1400 to 4100 and 3300 nmol/100 g/10 min. The bile flow observed with BSP plus CA was not significantly different from that with BSP plus DCA. The biliary excretion of total BSP was higher throughout with CA than with DCA because CA increased the biliary concentration of PSP while DCA did not. The bile flow attained with CA alone was significantly lower than that with BSP plus CA. The current data provide arguments for abandoning the view that choleresis per se is the crucial determinant for BSP excretion. When BSP-GSH was infused instead of BSP, the excretion rate of the dye was not altered by the additional infusion of CA whereas it was significantly reduced by DCA. The maximal biliary concentration of BSP-GSH fell from 25.9 nmol/mul to 15.3 and 9.4 nmol/mul with CA and DCA, respectively. Both CA and DCA impaired the hepatic uptake of BSP and BSP-GSH. During the infusion with CA, BSP plus CA and BSP-GSH plus CA the biliary excretion rates of bile acids did not differ significantly from each other. This favours the view that the transfer for CA from the liver to bile is different from that for BSP and BSP-GSH. A fraction of bile fluid "independent of choleretics" (viz. of bile salts, BSP and BSP-GSH) is estimated and discussed in view of the different types of infusion.     

Inhibitory effects of ursodeoxycholic acid on the induction of nitric oxide synthase in vascular smooth muscle cells

The expression of inducible nitric oxide synthase (iNOS) and the resultant increased nitric oxide production are associated with endotoxemia and atherosclerotic lesions observed in transplant hearts or balloon-injured artery. Ursodeoxycholic acid has been shown to have cardiovascular protective effects, such as inhibition of the development of transplant arteriosclerosis, but its mechanism remains unclear. Here, we investigated the effects of ursodeoxycholic acid on nitric oxide production and the expression of iNOS in vascular smooth muscle cells isolated from adult rat aorta and rabbit coronary artery. Nitrite released from cells in the culture medium was measured with the Griess reaction. iNOS mRNA and protein were measured by Northern and Western blot analyses. Treatment with ursodeoxycholic acid (30-1000 microM) significantly inhibited lipopolysaccharide plus interferon-gamma-induced nitric oxide production in a concentration-dependent manner, but ursodeoxycholic acid showed only small inhibitory effects on nitric oxide production that had already been induced by lipopolysaccharide plus interferon-gamma. Ursodeoxycholic acid by itself did not affect basal nitric oxide production. Ursodeoxycholic acid also suppressed lipopolysaccharide plus interferon-gamma-induced expression of iNOS mRNA and protein. Ursodeoxycholic acid had the most potent inhibitory effect among various kinds of bile acids examined, i.e. chenodeoxycholic acid, deoxycholic acid, cholic acid and conjugated bile acids such as tauroursodeoxycholic acid. These results suggest that ursodeoxycholic acid inhibits the induction of iNOS and then nitric oxide production in aortic and coronary artery smooth muscle cells, suggesting a possible mechanism for the cardiovascular protective effect of ursodeoxycholic acid under various pathophysiological conditions such as endotoxemia and atherosclerosis.     

RP-HPLC法测定熊去氧胆酸胶囊中熊去氧胆酸及有关物质的含量

目的建立反相高效液相色谱法(RP-HPLC)测定熊去氧胆酸胶囊中熊去氧胆酸、胆酸、鹅去氧胆酸及胆石酸的含量。方法使用Diamonsil C18色谱柱(200 mm×4.6 mm,5μm),流动相为乙腈-0.03 mol·L-1磷酸溶液(体积比为40∶60),流速为1.4 mL·min-1,检测波长为205 nm,柱温为35℃。结果熊去氧胆酸胶囊中熊去氧胆酸、胆酸、鹅去氧胆酸及胆石酸在25 min内洗脱并基线分离。熊去氧胆酸、胆酸、鹅去氧胆酸及胆石酸的线性范围分别为0.80²00.00、0.45200.00、0.45¹10.00、0.30110.00、0.30⁷0.00和0.3070.00和0.30⁸0.00 mg·L-1,平均回收率分别为99.7%、99.3%、98.7%和99.1%,RSD分别为1.30%、1.47%、1.87%和1.95%(n=3)。结论 RP-HPLC可用于同时测定熊去氧胆酸胶囊中熊去氧胆酸、胆酸、鹅去氧胆酸及胆石酸的含量,可应用于熊去氧胆酸胶囊胶囊制剂的质量控制。     

The Influence of 2-Hydroxypropyl-β-cyclodextrin on the Haemolysis Induced by Bile Acids

Cyclodextrins improve the water-solubility of drugs and can mask their haemolytic effect in parenteral use. Because the mechanism by which bile acids induce haemolysis is poorly understood, it has been investigated in the presence of 2-hydroxypropyl-β-cyclodextrin (HP-β-CyD). The haemolytic effect of 1.8 mm solutions of cholic acid, chenodeoxycholic acid (CDCA), deoxycholic acid and ursodeoxycholic acid (UDCA) in isotonic buffer at pH 7.4 was investigated at 37°C in the presence of HP-β-CyD at concentrations from 0.18 to 32 mm . No haemolytic effect was evident for cholic acid and UDCA. The haemolytic effect of the other bile acids was reduced by addition of HP-β-CyD and was prevented at a molar ratio of 1:1 owing to complex formation. An HP-β-CyD:bile acid molar ratio greater than 5:1 had a different effect on the erythrocyte membrane, irrespective of the identity of the bile acid; the effect was in accordance with the complexion affinities. In the absence of HP-β-CyD, the haemolytic effect of CDCA and deoxycholic acid appeared related to their capacity to form a surface monolayer and to solubilize the components of the erythrocyte membrane. The haemolytic effect observed after complexation of the bile acids appeared to be solely the effect of HP-β-CyD, which was able to form a reversible inclusion complex with lipophilic components of the erythrocyte membranes at concentrations higher than 12 mm .     

Quantitative relationship between bile acid structure and biliary lipid secretion in rats

A series of unconjugated and taurine conjugated bile acids (BAs) differing in water solubility (SWo), critical micellar concentration (CMC), and hydrophilicity (K') were infused iv to rats at a tracer dose and a dose of 6 mumol/min/kg over a 1-h period. Bile was collected for 3 h to evaluate the role of BA structure on cholesterol, phospholipids secretions, and bile flow. The BAs studied differ in the number (2-3), position (-3, -6, -7, -12), and orientation of the hydroxyls (alpha/beta); the side chain structure was modified by shortening (C-23, nor-BA) and by lengthening (C-25, homo-BA), while maintaining the same structure of nuclear hydroxyls (3 alpha 7 beta). At a "tracer" dose, all C-24 natural BAs are efficiently recovered in bile when administered in both unconjugated and taurine conjugated forms. At a "high dose", all taurine conjugated BAs are efficiently recovered in bile (80-100%). However, a variable recovery was observed among unconjugated BAs: trihydroxy BAs are efficiently recovered (85-100%), while dihydroxy BAs are only partially recovered (25-40%). The side chain-modified BAs [i.e., C-23 nor and C-25 homo analogs of ursodeoxycholic acid (UDCA)] are partially recovered at a tracer dose (20-30%), but less at a high dose (10-20%) when administered in the unconjugated form. In contrast, the corresponding taurine conjugates are more efficiently recovered in bile (60-80%). Conjugation with taurine increases total recovery of unconjugated BAs in bile by not more than 30-40%. Highly hydrophilic and water-soluble BAs, such as ursocholic acid (SWo = 1.67 mM) and cholic acid (SWo = 0.27 mM), can also be secreted as unconjugates, and this accounts for their complete recovery. The conjugation step is rate limiting for poorly soluble BAs such as ursodeoxycholic acid (SWo = 0.009 mM) when administered at a high dose, and critical for nor and homo analogs which are poorly soluble and whose side chain modification partially suppresses their conjugation with taurine or glycine and thereby induces alternative pathways such as glucuronidation or sulfation. The induced bile flow is directly related to the hydrophilicity of the natural C-24 bile acid.(ABSTRACT TRUNCATED AT 400 WORDS)