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Regulation of drug transporters by the farnesoid X receptor in mice.

The farnesoid X receptor (FXR, NR1H4) regulates bile acid and lipid homeostasis by acting as an intracellular bile acid-sensing transcription factor, resulting in altered expression of enzymes and transporters involved in bile acid synthesis and transport. Here, we quantitatively analyzed the alterations in expression levels of drug transporters, mainly organic anion-transporting polypeptides (oatp), in wild-type and FXR-null mice to evaluate the role of FXR in their expression and regulation by cholic acid. Changes in the mRNA amounts in liver, kidney, small intestine, and testis in FXR-null mice fed with or without a supplement of 0.5% cholic acid in the diet were analyzed by semiquantitative RT-PCR. In FXR-null mice, the mRNA levels of oatp1, oatp2, oatp3, and octn1 were lower than those of wild-type mice in kidney and testis, while there was no difference in liver or small intestine. Cholic acid feeding led to significantly decreased levels of expression of oatp1 and oct1 and an increased level of expression of oatp2 in wild-type mouse liver. In FXR-null mice, oatp1 and other transporters were downregulated in liver, kidney, and testis, whereas small intestine ASBT, octn2, and pept1 were upregulated. Our results suggested that FXR is involved in the transcriptional regulation of oatp and other transporters in a tissue-specific manner. Furthermore, the effect of cholic acid treatment indicates the involvement of regulatory mechanism(s) other than FXR.

Animals↗

Evidence for bile acid glucosides as normal constituents in human urine.

A glucosyltransferase catalysing formation of bile acid glucosides was recently isolated from human liver microsomes. In order to investigate the potential occurrence of such bile acid derivatives in vivo, a method was devised for their isolation and purification from urine. Conditions were established with the aid of glucosides of radiolabelled, unconjugated glycine and taurine conjugated bile acids prepared enzymatically using human liver microsomes. Analysis by gas chromatography and mass spectrometry of methyl ester trimethylsilyl ether derivatives indicated the excretion of glucosides of nonamidated hyodeoxycholic, chenodeoxycholic, deoxycholic, ursodeoxycholic and cholic acids and of glycine and taurine conjugated chenodeoxycholic and cholic acids. Additional compounds were present giving mass spectral fragmentation patterns typical of di- and trihydroxy bile acid glycosides. Semiquantitative estimates indicated a total daily excretion of about 1 mumol.

Bile Acids and Salts↗

Transgenic overexpression of human lecithin: cholesterol acyltransferase (LCAT) in mice does not increase aortic cholesterol deposition.

Results from several atherosclerosis studies using morphometric procedures have proven controversial with regard to whether over-expression of human LCAT in transgenic (Tg) mice is atherogenic. The purpose of the present study was to determine the effect of 10-fold over-expression of human LCAT on aortic free and esterified cholesterol (EC) deposition as well as plasma lipoprotein cholesteryl ester (CE) fatty acid composition in mice fed an atherogenic diet containing cholic acid. C57Bl/6 (control) and human LCAT-Tg mice were fed chow or an atherogenic diet (15% of calories from palm oil, 1.0% cholesterol and 0.5% cholic acid) for 24 weeks before measurement of aortic cholesterol content. Compared with the chow diet, control and LCAT-Tg mice fed the atherogenic diet had a 2-fold increase in plasma total, free and EC, a 7-fold increase in plasma apoB lipoprotein cholesterol, and a 40-50-fold increase in hepatic cholesterol content. The aortic EC content was increased in control (0.7 vs. 1.2 mg/g protein) and LCAT-Tg (0.3 vs. 1.5 mg/g protein) mice fed the atherogenic diet compared with those consuming the chow diet; however, there was no difference in aortic free (14.4+/-6.8 vs. 18.5+/-7.7 mg/g protein) or esterified (1.2+/-1.0 vs. 1.5+/-1.2 mg/g protein) cholesterol content between atherogenic diet-fed control and LCAT-Tg mice, respectively. LCAT-Tg mice fed the atherogenic diet had a 2-fold increase in the ratio of saturated+monounsaturated to polyunsaturated CE species in plasma apoB lipoproteins compared with control mice (9.4+/-2.4 vs. 4.9+/-0.7). We conclude that over-expression of human LCAT in Tg mice fed an atherogenic diet containing cholic acid does not result in increased aortic cholesterol deposition compared with control mice, even though the CE fatty acid saturation index of plasma apoB lipoproteins was doubled.

Analysis of Variance↗

Altered bile acid metabolism in nonobese, spontaneously diabetic (NOD) mice.

Cholesterol and bile acid metabolism was examined in nonobese, spontaneously diabetic (NOD) female mice before and after the development of diabetes. After the development of glucosuria, the plasma and liver cholesterol levels, gallbladder bile weight after 5-h fasting, biliary cholesterol, phospholipid and bile acid concentrations, the lithogenic index, the pool size of bile acids, and fecal sterol excretion markedly increased, but fecal bile acid excretion and fractional turnover rates for the cholic acid and chenodeoxycholic acid groups decreased. The distribution percentage of bile acids in the small intestine did not change, but it increased in the gallbladder and decreased in the large intestine. One striking finding was a change in the bile acid composition: increases were recorded in cholic and deoxycholic acids while decreases occurred in bile acids derived from chenodeoxycholic acid, such as beta-muricholic and ursodeoxycholic acids in the bile and alpha-muricholic, beta-muricholic, omega-muricholic, and hyodeoxycholic acids in the feces. Therefore, the cholic acid group/chenodeoxycholic acid group (CA/CDCA) ratio increased in the bile, feces, and small and large intestines after the development of diabetes. These changes were very similar to those observed in alloxan-treated mice, suggesting that the changes found in NOD mice are caused by insulin deficiency.

Animals↗

Potential bile acid metabolites. 17. Synthesis of 2 beta-hydroxylated bile acids.

The 2 beta-hydroxylated derivatives of lithocholic, chenodeoxycholic, deoxycholic, and cholic acids were synthesized from the respective parent bile acids by established procedures. The principal reactions involved were (1) bromination of 3-oxo formylated bile acids in N,N-dimethylformamide, (2) rearrangement and substitution of the resulting 4 beta-bromo-3-oxo derivatives to the 2 beta-acetoxy-3-oxo compounds with potassium acetate, and (3) reduction to the 2 beta-acetoxy-3 alpha-hydroxy compounds with tert-butylamine-borane complex. As for the prepared 2 beta-hydroxylated bile acids with a diequatorial trans-glycol structure, proton and carbon-13 nuclear magnetic resonance spectroscopic and gas-liquid chromatographic/mass spectrometric properties are discussed.

Acetates↗

Rabbit ileal mucosa exposed to fatty acids, bile acids, and other secretagogues. Scanning electron microscopic appearances.

Segments of rabbit ileum were examined by scanning electron microscopy (SEM) after exposure to various compounds known to stimulate fluid secretion in the small intestine. After perfusion with ricinoleate (castor oil) at a 10 mM concentration, striking changes were observed at villus tips and on the apicolateral surfaces of villi; erosions at tips were confirmed by light microscopy of the same pieces of tissue examined by SEM. The appearances after ricinoleate were reversed in part during perfusion with control buffer for 2 hr. Statistical comparisons between control perfused, treated, and reversal tissues showed that the "damage" produced by ricinoleate, and its reversal, was significant statistically. Tissues treated with other intestinal secretagogues, oleic acid (10 mM), deoxycholic acid (4 mM), cholic acid (4 mM), dioctyl sodium sulfosuccinate (6 mM), and cholera toxin (1 microgram/ml) also showed surface changes by SEM. Fluid secretion, produced by an osmotic agent (mannitol) was not associated with "damage." Changes in structure of the mucosal surface after exposure to intestinal secretagogues should be considered as one possible mechanism of impaired fluid transport.

Animals↗

Dissolution of cholesterol gallstones by bile acids in hamsters.

UNLABELLED: We previously reported a hamster model for cholesterol gallstone formation and prophylaxis. The aim of this study was to validate a model for dissolution of cholesterol gallstones by testing bile acids used in patients. Sixty hamsters were allocated to six groups of ten; Group I received the standard diet (.8mg cholesterol/gram food) and Groups II-VI received the lithogenic regime (2.4 mg cholesterol/gram food and 15 micrograms ethinyl estradiol) for twelve weeks. During the next eight weeks, Group I remained on the standard diet, Group II on the lithogenic regime, while Group III switched to the standard diet. Groups IV-VI remained on the lithogenic regime, and received 20 mg/kg/d of CDC (Group IV), UDC (Group V) or cholic acid (Group VI). Cholesterol gallstones were found in 90% of hamsters on the lithogenic regime, even after return to the standard diet, in 80% of those receiving cholic acid, and in none receiving the standard diet, CDC or UDC. CDC and UDC but not cholic acid inhibited hepatic HMG-CoA reductase activity (p less than 0.01) and desaturated bile (p less than 0.01). The highest HMG-CoA reductase (p less than 0.02) occurred after return from the lithogenic regime to the standard diet. CONCLUSIONS: 1) A new model for cholesterol gallstone dissolution has been validated; 2) CDC and UDC, in contrast to cholic acid, decreased HMG-CoA reductase, desaturated bile and dissolved gallstones as in patients; and 3) Return from the lithogenic regime to the standard diet did not desaturate bile or dissolve gallstones, but did increase HMG-CoA reductase as found in gallstone patients.

Animals↗

Cholestyramine treatment reduces postprandial but not fasting serum bile acid levels in humans.

Fasting serum concentrations of cholic acid, chenodeoxycholic acid, and deoxycholic acid were determined in healthy subjects and in patients with familial hypercholesterolemia before and during treatment with cholestyramine. The bile acids were analyzed by a specific isotope-dilution technique by using gas chromatography-mass spectrometry. Cholestyramine treatment did not change the fasting concentration of total bile acids, but the contribution of cholic acid was increased; those of chenodeoxycholic acid and deoxycholic acid were decreased. No decrease of fasting bile-acid concentrations in portal venous serum was seen in 2 cholestyramine-treated gallstone patients. The postprandial total bile-acid concentration was about 40% lower during cholestyramine treatment in healthy subjects, reflecting a reduced postprandial inflow of bile acids to the liver. This degree of interruption of the postprandial enterohepatic circulation may be sufficient to produce a near maximal bile-acid biosynthesis rate and to promote lowering of plasma cholesterol also in the fasting state. It is concluded that the postprandial bile-acid inflow to the liver may be more important as a regulator of bile-acid biosynthesis than is the fasting level of bile acids.

Bile Acids and Salts↗

Bile acid kinetics in relation to endogenous tryglyceride metabolism in various types of hyperlipoproteinemia.

Bile acid and plasma endogenous triglyceride kinetics were determined under standardized dietary conditions in 47 hyperlipidemic subjects with the aid of [14C]cholic acid, [14C]chenodeoxycholic acid, and [3H]glycerol, respectively. On the basis of their lipoprotein pattern the patients were separated into three groups characterized by hyperlipoproteinemia (HLP) type IIa (n = 19), type IIb (n = 6), and type IV (n = 22). In keeping with previous reports from this laboratory the total bile acid formation reports from this laboratory the total bile acid formation in HLP type IV (19.5 +/- 2.2) mumol kg-1d-1, mean +/- SEM) exceeded that encountered in type IIa (10.7 +/- 0.9 mumol kg-1d-1, P less than 0.005). This difference was mainly due to an increased synthesis of cholic acid in type IV HLP (12.7 +/- 1.7 mumol kg-1d-1 vs. 6.1 +/- 0.5 mumol kg-1d-1, P less than 0.005). Bile acid formation in type IIb HLP was essentially within the limits recorded for type IIa. Apparent plasma triglyceride formation (as calculated from the 10-hr radioactivity decay curve) averaged 10.5 +/- 0.7 mumol kg-1hr-1 in type IIa HLP and was significantly higher in type IIb (20.7 +/- 1.9 mumol kg-1hr-1, P less than 0.001) and in type IV (22.1 +/- 1.4 mumol kg-1hr-1, P less than 0.001). The apparent fractional turnover rate of plasma triglyceride in type IV HLP (0.147 +/- 0.011 hr-1) was lower than that encountered in type IIa (0.188 +/- 0.008, P less than 0.01) and in type IIb (0.177 +/- 0.011 hr-1). The apparent production of plasma triglycerides and the formation of cholic acid correlated in type IIa (r = +0.69, P less than 0.001) and in type IV HLP (r = +0.70, P less than 0.001). A similar pattern was seen for total bile acid formation, while chenodeoxycholic acid showed a correlation to apparent triglyceride synthesis only in type IV HLP. It is suggested that an increased formation of plasma triglycerides--monitoring very low density lipoprotein synthesis--is linked to an enhanced degradation of cholesterol to bile acids and that there is an integrated regulation of the metabolism of these two parameters.

Adult↗

A critical evaluation of a procedure for measurement of serum bile acids by radioimmunioassay.

A radioimmunoassay for the quantitative determination of cholic acid conjugates has been developed. Antisera were raised in rabbits injected with cholylglycine coupled by amide linkage to bovine serum albumin. The antibodies reported in this communication were not found to be mono-specific in the strictest sense. This assay is relatively simple, rapid, sensitive, reliable, and most importantly, specific for bile acids; the specificity of each antibody, however, must be thoroughly characterized at the dilution in routine use. The range of normal values for cholic acid conjugates in serum was found to be 0.1--1.6 micronmol/l (mean: 0.62, +/- S.D.: 0.4).

Animals↗

Enrichment of the more hydrophilic bile acid ursodeoxycholic acid in the fecal water-soluble fraction after feeding to rats with colon polyps.

We recently showed that feeding the cytoprotective bile acid ursodeoxycholic acid (UDCA) to rats resulted in significant reduction in polyps and especially cancers, both in number and size (D. L. Earnest et al., Cancer Res., 54: 5071-5074, 1994). Because fecal secondary bile acids [particularly deoxycholic acid (DCA)] are considered to promote formation of colon adenomas and cancer, we have now attempted to find a relationship between polyp reduction and fecal secondary bile acids after feeding UDCA to these rats. We examined the fecal bile acids in rats with polyps and compared them with fecal bile acids in control rats and also determined the bile acid composition in fecal aqueous phase, which is in direct contact with the colon epithelium and may be physiologically more active. Treatment with azoxymethane did not significantly alter fecal bile acid composition in the rats. Cholic acid feeding resulted in greatly increased proportions of DCA (82% of total bile acids versus 18% in control rats). On the other hand, UDCA feeding significantly reduced the proportion of fecal DCA (2% in control rats fed UDCA and 3% in rats also treated with azoxymethane). In control rats, 96% of the bile acids were present in the water-insoluble fraction and 4% in the water-soluble fraction. The major insoluble bile acids included DCA and hyodeoxycholic acid (73% of total bile acids). In contrast, the muricholic acids were concentrated in the soluble fraction (37%). When 0.4% UDCA was added to the diet, lithocholic acid increased in the insoluble fraction (40 versus 1%), but the hydrophilic UDCA and muricholic acids were enriched in the water-soluble fraction (37 and 43%, respectively). Thus, the hydrophobic bile acids were distributed predominantly in the water-insoluble fraction, whereas the hydrophilic bile acids were distributed preferentially in the water-soluble fraction. These data suggest that UDCA may prevent colon tumors and polyps by countering the toxic effect of DCA and enhancing the possible cytoprotective effects of UDCA and muricholic acids in the water-soluble fraction in the feces of rat.

Animals↗

Effects of low dose chenodeoxycholic acid feeding on biliary lipid metabolism.

To better define the mechanisms by which chenodeoxycholic acid (CDCA) alters the lipid composition of bile and promotes dissolution of cholesterol gallstones, we have studied the effects of relatively low doses of CDCA on the metabolism of biliary lipids in 10 subjects without gallstones. In 5 subjects, the effects of CDCA feeding were compared to those of cholic acid, a bile acid that apparently does not dissolve cholesterol stones. The following measurements were carried out during control and treatment periods: (1) composition of biliary lipids, (2) hepatic secretion rates of biliary lipids, (3) pool sizes of bile acids, and (4) specific composition of bile acids. Low doses of CDCA consistently reduced the lithogenicity of gallbladder bile by decreasing the proportion of cholesterol relative to the solubilizing lipids--bile acids and lecithin. This decrease in lithogenicity was associated with a selective reduction in hepatic secretion rates of cholesterol. At the doses of CDCA given, secretion rates of bile acids and lecithin and pool sizes of bile acids were not significantly changed; also conversion of cholesterol into bile acids was not completely inhibited. Cholic acid feeding appeared to increase the total size of the bile acid pool, but it did not affect the lithogenicity of bile or secretion rates of cholesterol. The data show that at low doses CDCA lowers lithogenicity of bile by reducing hepatic secretion of cholesterol, while cholic acid does not have a similar effect.

Bile↗

Effect of diabetes and of 7 alpha-hydroxycholesterol infusion on the profile of bile acids secreted by the isolated rat livers.

The isolated livers from normal, streptozotocin-diabetic, and insulin-treated diabetic rats were perfused without and with infused 7 alpha-hydroxycholesterol. Biliary bile acids were extracted and analysed by gas chromatography. In each liver group, total bile acid concentration was more than four times greater with infused 7 alpha-hydroxycholesterol than without the sterol. Without infused 7 alpha-hydroxycholesterol, bile acids in the control group were composed mainly of beta-muricholic acid and to a lesser extent of cholic acid. In the diabetic group, the ratio between these two bile acids reversed. The ratio tended to be normalized by treatment with insulin. With infused 7 alpha-hydroxycholesterol, the control group secreted chenodeoxycholic acid at a considerable higher percentage besides major beta-muricholic acid and minor cholic acid. In the diabetic group, the ratio between the latter two bile acids reversed as was the case with the endogenous secretion, while the percentage of chenodeoxycholic acid remained then unchanged. The diminished percentage of beta-muricholic acid in the diabetic group was increased two times by treatment with insulin.

Animals↗

Cholecystokinin prophylaxis of parenteral nutrition-induced gallbladder disease.

Recent studies indicate that long-term total parenteral nutrition (TPN) induces gallstone formation and acalculous cholecystitis in humans. Cholecystectomy is hazardous for these patients because they frequently have multiple medical problems and have undergone numerous abdominal operations. The present study was designed to develop a method to prevent TPN-induced gallbladder disease. The authors tested the hypothesis that a single daily intravenous infusion of cholecystokinin-octapeptide (CCK-OP) will prevent TPN-induced gallbladder stasis. Eleven prairie dogs received TPN for 10 days. Six of these animals were given a daily infusion of CCK-OP. Control animals were fed ad lib. Each animal's bile salt pool was labeled with intravenous 3H-cholic acid 16 hours prior to acute terminal experiments. The ratio of gallbladder to hepatic bile 3H-cholic acid specific activity (Rsa) provides an index of gallbladder stasis. A Rsa of less than 1.0 indicates gallbladder stasis. TPN animals had a Rsa of 0.54 +/- 0.13 (p less than 0.01 vs. controls), indicating stasis of bile in the gallbladder. Daily CCK-OP infusions resulted in a Rsa of 0.92 +/- 0.10 (p less than 0.05 vs. TPN without CCK-OP), indicating that TPN-induced gallbladder stasis is prevented by daily CCK-OP. Control animals had a Rsa of 1.03 +/- 0.06. The cholesterol saturation indices of gallbladder and hepatic bile were not increased by TPN or CCK-OP. These data indicate that 1) TPN induces gallbladder stasis but does not increase bile lithogenic index; and 2) daily injections of CCK-OP prevent TPN-induced gallbladder stasis.

Animals↗

Diagnostic value of serum immunoreactive conjugated cholic or chenodeoxycholic acids in detecting hepatobiliary diseases. Comparison with levels of 3 alpha-hydroxy bile acids determined enzymatically and with routine liver tests.

The diagnostic value of the enzymatic fluorometric method for total serum bile acids (TSBA) and for radioimmunoassay measurement for conjugated cholic acid (CCA) or chenodeoxycholic acid was compared with that of routine liver function tests in 223 patients with liver disease, 88 healthy subjects, and 118 patients affected by other diseases. The value of the tests for screening in the general population was assessed by simulation, using estimates of disease prevalence. TSBA was significantly more sensitive (78%) but less specific (94%) than CCA (sensitivity of 69%, specificity of 98%). Aspartate aminotransferase was nearly as sensitive (74%) as TSBA, but significantly less specific (93%) than CCA. CCA provided the highest positive predictivity (98%), even in a screening simulation (32%). With the use of sequential aspartate aminotransferase measurement followed by CCA, this value rose to 100%. This test procedure appears to be the best screening method for liver diseases available at present.

Adolescent↗

Binding of bile acids by glutathione S-transferases from rat liver.

Binding of bile acids and their sulfates and glucuronides by purified GSH S-transferases from rat liver was studied by 1-anilino-8-naphthalenesulfonate fluorescence inhibition, flow dialysis, and equilibrium dialysis. In addition, corticosterone and sulfobromophthalein (BSP) binding were studied by equilibrium and flow dialysis. Transferases YaYa and YaYc had comparable affinity for lithocholic (Kd approximately 0.2 microM), glycochenodeoxycholic (Kd approximately to 60 microM), and cholic acid (Kd approximately equal 60 microM), and BSP (Kd approximately 0.09 microM). YaYc had one and YaYa had two high affinity binding sites for these ligands. Transferases containing the Yb subunit had two binding sites for these bile acids, although binding affinity for lithocholic acid (Kd approximately 4 microM) was lower than that of transferases with Ya subunit, and binding affinities for the other bile acids were comparable to the Ya family. Sulfated bile acids were bound with higher affinity and glucuronidated bile acids with lower affinity by YaYa and YaYc than the respective parent bile acids. In the presence of GSH, binding of lithocholate by YaYc was unchanged and binding by YbYb' was inhibited. Conversely, GSH inhibited the binding of cholic acid by YaYc but had less effect on binding by YbYb'. Cholic acid did not inhibit the binding of lithocholic acid by YaYa.

Anilino Naphthalenesulfonates↗

The role of glucocorticoids in the regulation of the diurnal rhythm of hepatic beta-hydroxy-beta-methylglutaryl-coenzyme A reductase and cholesterol 7 alpha-hydroxylase.

The microsomal activities of the hepatic enzymes hydroxymethylglutaryl-CoA reductase and cholesterol 7 alpha-hydroxylase exhibit a diurnal rhythm with maximum activities observed during the dark period and minimum activities around noon (12:00h). This diurnal rhythm was maintained for both enzymes after adrenalectomy, but the amplitude of variation for the activity of both enzymes was greatly decreased. A single injection of cortisol administered to adrenalectomized rats 3h before the expected maximum in enzyme activity resulted in a twofold increase in the activity of both enzymes 3h later, at values similar to those observed for control rats killed at the same time. This response appeared to require protein synthesis, since it was blocked by actinomycin D. However, the administration of cortisol to adrenalectomized rats 3 h before the expected minimum did not result in significant change in the activity of hydroxymethylglutaryl-CoA reductase and cholesterol 7 alpha-hydroxylase 3 h later. Kinetic studies of cholic acid metabolism in vivo demonstrated that adrenalectomy results in a significant decrease in the rate of synthesis of cholic acid and a considerable decrease in the pool size of cholic acid and its metabolic products. Treatment of adrenalectomized rats with cortisol increased the rate oonsistent with the effects of adrenalectomy and cortisol treatment on the activity of cholesterol 7alpha-hydroxylase.

Adrenalectomy↗