Endogenous Bile Acid Synthesis Research Articles

A Transient Inflammatory Response Induced by Lipopolysaccharide Infusion Lowers Markers of Endogenous Cholesterol and Bile Acid Synthesis in Healthy Normocholesterolemic Young Men.

Inflammation is associated with changes in plasma lipids, lipoproteins, and cholesterol efflux capacity (CEC). It is unknown if the changes in lipids and lipoproteins during inflammation are related to changes in cholesterol absorption, synthesis, and bile acid synthesis. We, therefore, examined the effects of acute lipopolysaccharide (LPS)-induced transient systemic inflammation on lipids, lipoproteins, CEC, and markers of cholesterol metabolism. We also evaluated whether markers for cholesterol metabolism at baseline predict the intensity of the inflammatory response. Eight healthy young subjects received LPS infusion, and blood was sampled for the following 24 h. In addition to lipids, lipoproteins, and CEC, we also measured markers for cholesterol absorption and synthesis, bile acid synthesis, and inflammation. Compared with baseline, plasma total cholesterol, low-density lipoprotein cholesterol, and CEC decreased, while triglycerides increased in the 24 h following LPS infusion. TC-standardized levels of cholesterol synthesis markers (lathosterol, lanosterol, and desmosterol) and a bile acid synthesis marker (7α-OH-cholesterol) also decreased, with no changes in cholesterol absorption markers (campesterol, sitosterol, and cholestanol). Baseline TC-standardized levels of desmosterol and 7α-OH-cholesterol were positively correlated with concentrations of various inflammatory markers. Changes in TC-standardized desmosterol and 7α-OH-cholesterol were negatively correlated with concentrations of inflammatory markers. LPS infusion reduced endogenous cholesterol synthesis and bile acid synthesis in healthy young men.

Δ4-3-oxosteroid-5β-reductase deficiency: Responses to oral bile acid therapy and long-term outcomes.

BACKGROUNDDisorders of primary bile acid synthesis may be life-threatening if undiagnosed, or not treated with primary bile acid replacement therapy. To date, there are few reports on the management and follow-up of patients with Δ4-3-oxosteroid 5β-reductase (AKR1D1) deficiency. We hypothesized that a retrospective analysis of the responses to oral bile acid replacement therapy with chenodeoxycholic acid (CDCA) in patients with this bile acid synthesis disorder will increase our understanding of the disease progression and permit evaluation of this treatment regimen as an alternative to the Food and Drug Administration (FDA) approved drug cholic acid, which is currently unavailable in China.AIMTo evaluate the therapeutic responses of patients with AKR1D1 deficiency to oral bile acid therapy, specifically CDCA.METHODSTwelve patients with AKR1D1 deficiency, confirmed by fast atom bombardment ionization-mass spectrometry analysis of urine and by gene sequencing for mutations in AKR1D1, were treated with differing doses of CDCA or ursodeoxycholic acid (UDCA). The clinical and biochemical responses to therapy were monitored over a period ranging 0.5-6.4 years. Dose adjustment, to optimize the therapeutic dose, was based on changes in serum biochemistry parameters, notably liver function tests, and suppression of the urinary levels of atypical hepatotoxic 3-oxo-Δ4-bile acids measured by mass spectrometry.RESULTSPhysical examination, serum biochemistry parameters, and sonographic findings improved in all 12 patients during bile acid therapy, except one who underwent liver transplantation. Urine bile acid analysis confirmed a significant reduction in atypical hepatotoxic 3-oxo-Δ4 bile acids concomitant with clinical and biochemical improvements in those patients treated with CDCA. UDCA was ineffective in down-regulating endogenous bile acid synthesis as evidenced from the inability to suppress the urinary excretion of atypical 3-oxo-Δ4-bile acids. The dose of CDCA required for optimal clinical and biochemical responses varied from 5.5-10 mg/kg per day among patients based on maximum suppression of the atypical bile acids and improvement in serum biochemistry parameters, and careful titration of the dose was necessary to avoid side effects from CDCA.CONCLUSIONThe primary bile acid CDCA is effective in treating AKR1D1 deficiency but the therapeutic dose requires individualized optimization. UDCA is not recommended for long-term management.

FXR-Dependent Modulation of the Human Small Intestinal Microbiome by the Bile Acid Derivative Obeticholic Acid

Intestinal bacteria can modify the composition of bile acids and bile acids, which are regulated by the farnesoid X receptor, affect the survival and growth of gut bacteria. We studied the effects of obeticholic acid (OCA), a bile acid analogue and farnesoid X receptor agonist, on the intestinal microbiomes of humans and mice. We performed a phase I study in 24 healthy volunteers given OCA (5, 10, or 25 mg/d for 17 days). Fecal and plasma specimens were collected at baseline (day 0) and on days 17 (end of dosing) and 37 (end of study). The fecal specimens were analyzed by shotgun meta-genomic sequencing. A Uniref90 high-stringency genomic analysis was used to assign specific genes to the taxonomic signature of bacteria whose abundance was associated with OCA. Male C57BL/6 mice were gavage fed daily with water, vehicle, or OCA (10 mg/kg) for 2 weeks. Small intestine luminal contents were collected by flushing with saline and fecal pellets were collected at baseline and day 14. Mouse samples were analyzed by 16S-tagged sequencing. Culture experiments were performed to determine the taxonomic-specific effects of bile acids and OCA on bacterial growth. Suppression of endogenous bile acid synthesis by OCA in subjects led to a reversible induction of gram-positive bacteria that are found in the small intestine and are components of the diet and oral microbiota. We found that bile acids decreased proliferation of these bacteria in minimum inhibitory concentration assays. In these organisms, there was an increase in the representation of microbial genomic pathways involved in DNA synthesis and amino acid metabolism with OCA treatment of subjects. Consistent with these findings, mice fed OCA had lower endogenous bile acid levels and an increased proportion of Firmicutes, specifically in the small intestine, compared with mice fed water or vehicle. In studying the effects of OCA in humans and mice, we found evidence for interactions between bile acids and features of the small intestinal microbiome. These findings indicate that farnesoid X receptor activation alters the intestinal microbiota and could provide opportunities for microbiome biomarker discovery or new approaches to engineering the human microbiome. ClinicalTrials.gov, NCT01933503.

EP4 emerges as a novel regulator of bile acid synthesis and its activation protects against hypercholesterolemia

Prostaglandin E receptor subtype 4 (EP4) knockout mice develops spontaneous hypercholesterolemia but the detailed mechanisms by which EP4 affects cholesterol homeostasis remains unexplored. We sought to determine the cause of hypercholesterolemia in EP4 knockout mice, focusing on the role of EP4 in regulating the synthesis and elimination of cholesterol. Deficiency of EP4 significantly decreased total bile acid levels in the liver by 26.2% and the fecal bile acid content by 27.6% as compared to wild type littermates, indicating that the absence of EP4 decreased hepatic bile acid synthesis and their subsequent excretion in stools. EP4 deficiency negatively regulate bile acid synthesis through repression of phosphorylated extracellular signal-regulated kinase 1/2 (ERK)-mediated cholesterol 7α-hydroxylase (CYP7A1) expression and that the hypercholesterolemia in EP4 knockout mice is due to a defect in cholesterol conversion into bile acids. Deficiency of EP4 also increased de novo cholesterol synthesis and altered cholesterol fluxes in and out of the liver. Treating high fat diet-challenged mice with the pharmacological EP4 agonist, CAY10580 (200 μg/kg body weight/day i.p) for three weeks effectively prevented diet-induced hypercholesterolemia, enhanced endogenous bile acid synthesis and their fecal excretion. In summary, EP4 plays a critical role in maintaining cholesterol homeostasis by regulating the synthesis and elimination of bile acids. Activation of EP4 serves as an effective novel strategy to promote cholesterol disposal in the forms of bile acids in order to lower plasma cholesterol levels.

Lactation during cholestasis: Role of ABC proteins in bile acid traffic across the mammary gland

Transporters involved in bile acid (BA) handling by the mammary gland are poorly understood. Here we have investigated the role of ABC proteins in blood-milk BA traffic and its sensitivity to maternal cholestasis. BA concentrations in rat and mouse serum were higher than in milk. BA profiles in both fluids were also different. In mammary gland, mRNA levels of ABC pumps transporting BAs were high for Bcrp, less abundant for Mrp1, Mrp3 and Mrp4 and negligible for Bsep and Mrp2. Milk BA concentrations were lower in Abcg2−/− than in wild-type mice. Taurocholate administration (5 µmol, i.p.) increased 20-fold BA concentrations in serum, but only moderately in milk, even in Abcg2−/− mice. Bile duct ligation (BDL) in pregnant rats markedly increased serum BA concentrations, which was not proportionally reflected in milk. In rat mammary tissue, Mrp4 was up-regulated by BDL. Serum BA levels were 2-fold higher in 10-day-old neonates of the BDL group, whereas their body weight was lower. The exchange of breastfeeding mothers immediately after birth reverted the situation without changes in endogenous BA synthesis. In conclusion, Bcrp is involved in BA secretion into milk, whereas Mrp4 participates in a blood-milk barrier that protects neonates from maternal hypercholanemia during breastfeeding.

Increased serum bile acid concentration following low-dose chronic administration of thioacetamide in rats, as evidenced by metabolomic analysis

A liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS)-based metabolomics approach was employed to identify endogenous metabolites as potential biomarkers for thioacetamide (TAA)-induced liver injury. TAA (10 and 30mg/kg), a well-known hepatotoxic agent, was administered daily to male Sprague–Dawley (SD) rats for 28days. We then conducted untargeted analyses of endogenous serum and liver metabolites. Partial least squares discriminant analysis (PLS-DA) was performed on serum and liver samples to evaluate metabolites associated with TAA-induced perturbation. TAA administration resulted in altered levels of bile acids, acyl carnitines, and phospholipids in serum and in the liver. We subsequently demonstrated and confirmed the occurrence of compromised bile acid homeostasis. TAA treatment significantly increased serum levels of conjugated bile acids in a dose-dependent manner, which correlated well with toxicity. However, hepatic levels of these metabolites were not substantially changed. Gene expression profiling showed that the hepatic mRNA levels of Ntcp, Bsep, and Oatp1b2 were significantly suppressed, whereas those of basolateral Mrp3 and Mrp4 were increased. Decreased levels of Ntcp, Oatp1b2, and Ostα proteins in the liver were confirmed by western blot analysis. These results suggest that serum bile acids might be increased due to the inhibition of bile acid enterohepatic circulation rather than increased endogenous bile acid synthesis. Moreover, serum bile acids are a good indicator of TAA-induced hepatotoxicity.

Endosymbiotic Actinidic Archaeal Synthesis of Bile Acids from Cholesterol Regulates Cellular Function

Aims and Objectives: Endomyocardial fibrosis along with the root wilt disease of coconut is endemic to Kerala with its radioactive actinide beach sands. Actinides like rutile as well as organisms like phytoplasmas and viroids have been implicated in the etiology of these diseases. Bile acids has been related to the pathogenesis of schizophrenia, malignancy, metabolic syndrome x, autoimmune disease and neuronal degeneration. The possibility of endogenous bile acid synthesis by actinide based primitive organism like archaea with a mevalonate pathway and cholesterol catabolism was considered in these disease states. Methodology: Plasma from fasting heparinised blood was used and the experimental protocol was as follows (I) Plasma+phosphate buffered saline, (II) same as I+cholesterol substrate, (III) same as II+rutile 0.1 mg/ml, (IV) same as II+ciprofloxacine and doxycycline each in a concentration of 1 mg/ml. The following estimations were carried out:- Cytochrome F420 and bile acids. Results: Plasma of control subjects showed increased levels of the above mentioned parameters with after incubation for 1 hour and addition of cholesterol substrate resulted in still further significant increase in these parameters. The plasma of patients showed similar results but the extent of increase was more. The addition of antibiotics to the control plasma caused a decrease in all the parameters while addition of rutile increased their levels. The addition of antibiotics and rutile to the patient’s plasma produced the same changes but the extent of change was more in patient’s sera as compared to controls. Conclusion: An actinide dependent shadow biosphere of archaea and viroids in the above mentioned disease states is described. The actinidic archaea synthesizes bile acids from cholesterol. The archaeal bile acids regulate neuro-immuno-endocrine functions and are important in disease pathogenesis. Key words : Archaea; actinides; bile acids; cholesterol

Effect of SLCO1B1 polymorphism on the plasma concentrations of bile acids and bile acid synthesis marker in humans

Organic anion transporting polypeptide 1B1 (OATP1B1, encoded by SLCO1B1) is a sinusoidal influx transporter of human hepatocytes. Our aim was to characterize the role of OATP1B1 in the hepatic uptake of bile acids in vivo. Fasting blood samples were drawn from 24 healthy volunteers with SLCO1B1 c.388AA-c.521TT (*1A/*1A) genotype, eight with c.388GG-c.521TT (*1B/*1B) genotype, 24 with c.521TC genotype, and nine with c.521CC genotype. Plasma concentrations of 15 endogenous bile acids, their synthesis marker, and cholesterol were determined by liquid chromatography-tandem mass spectrometry. The concentrations of ursodeoxycholic acid, glycoursodeoxycholic acid, chenodeoxycholic acid, and glycochenodeoxycholic acid were approximately 50-240% higher in individuals with the SLCO1B1 c.521CC, c.521TC, or c.388AA-c.521TT genotype than in those with the c.388GG-c.521TT genotype (P<0.05), with the largest differences seen between the c.521CC and c.388GG-c.521TT individuals. The concentration of tauroursodeoxycholic acid was approximately 120% higher in individuals with the c.521TC genotype and that of taurochenodeoxycholic acid 110% higher in individuals with the c.521CC or c.521TC genotype than in those with the c.388GG-c.521TT genotype (P<0.05). The cholic acid concentration was approximately 30% higher in individuals with the c.521CC or c.388AA-c.521TT genotype than in those with the c.388GG-c.521TT genotype (P<0.05), but its conjugates remained unaffected by the genotype. The bile acid synthesis marker 7alpha-hydroxy-4-cholesten-3-one/cholesterol concentration ratio was 62 or 45% higher in the c.388AA-c.521TT participants than in the c.388GG-c.521TT or c.521TC participants, respectively (P<0.05). SLCO1B1 polymorphism considerably affects the disposition of several endogenous bile acids and bile acid synthesis marker, indicating that OATP1B1 plays an important role in the hepatic uptake of bile acids in vivo in humans.

The lipid-lowering effect of ezetimibe in pure vegetarians

Results of previous studies have shown that ezetimibe (10 mg/day) reduces LDL cholesterol in patients with mild hypercholesterolemia on a normal-cholesterol diet (dietary intake of 200-500 mg/day) by 16-22%. However, the LDL cholesterol-lowering effect of ezetimibe in subjects with an extremely low dietary cholesterol intake (vegetarians) has not been studied. We conducted a randomized, double-blind, placebo-controlled, two-phase crossover study in 18 healthy pure vegetarians to assess the effect of ezetimibe (10 mg/day) on plasma lipids, cholesterol absorption, and its synthesis. Treatment periods lasted 2 weeks each, with an intervening 2 week washout period. Fractional cholesterol absorption was determined using the continuous dual stable isotope feeding method. Mean dietary cholesterol intake in the pure vegetarians was extremely low and averaged 29.4 +/- 16.8 and 31.4 +/- 14.4 mg/day during the placebo and ezetimibe administration phases, respectively. Fractional cholesterol absorption during the placebo phase was 48.2 +/- 8.2% and was decreased by 58% during ezetimibe treatment to 20.2 +/- 6.2% (P < 0.001). This change in intestinal cholesterol absorption was followed by a significant reduction in LDL cholesterol of 17.3%. In individuals with extremely low dietary cholesterol intake, treatment with ezetimibe (10 mg/day) leads to a significant reduction of cholesterol absorption and a clinically relevant decrease of plasma LDL cholesterol, comparable to that of subjects with a normal dietary cholesterol intake. Thus, the lipid-lowering effect of ezetimibe is mediated mainly through a reduction of the absorption of endogenous (biliary) cholesterol.

Complementary Stimulation of Hepatobiliary Transport and Detoxification Systems by Rifampicin and Ursodeoxycholic Acid in Humans

Rifampicin (RIFA) and ursodeoxycholic acid (UDCA) improve symptoms and biochemical markers of liver injury in cholestatic liver diseases by largely unknown mechanisms. We aimed to study the molecular mechanisms of action of these drugs in humans. Thirty otherwise healthy gallstone patients scheduled for cholestectomy were randomized to RIFA (600 mg/day for 1 week) or UDCA (1 g/day for 3 weeks) or no medication before surgery. Routine biochemistry, lipids, and surrogate markers for P450 activity (4beta-hydroxy cholesterol, 4beta-OH-C) and bile acid synthesis (7alpha-hydroxy-4-cholesten-3-one, C-4) were measured in serum. Bile acids were analyzed in serum, urine, and bile. A wedge liver biopsy specimen was taken to study expression of hepatobiliary ABC transporters as well as detoxification enzymes and regulatory transcription factors. RIFA enhanced bile acid detoxification as well as bilirubin conjugation and excretion as reflected by enhanced expression of CYP3A4, UGT1A1, and MRP2. These molecular effects were paralleled by decreased bilirubin and deoxycholic acid concentrations in serum and decreased lithocholic and deoxycholic acid concentrations in bile. UDCA on the other hand stimulated the expression of BSEP, MDR3, and MRP4. UDCA became the predominant bile acid after UDCA treatment and lowered the biliary cholesterol saturation index. RIFA enhances bile acid detoxification as well as bilirubin conjugation and export systems, whereas UDCA stimulates the expression of transporters for canalicular and basolateral bile acid export as well as the canalicular phospholipid flippase. These independent but complementary effects may justify a combination of both agents for the treatment of cholestatic liver diseases.

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.

Delta 22-Ursodeoxycholic acid, a unique metabolite of administered ursodeoxycholic acid in rats, indicating partial beta-oxidation as a major pathway for bile acid metabolism.

We describe for the first time the identification of 3 alpha, 7 beta-dihydroxy-5 beta-chol-22-en-24-oic acid (delta 22-UDCA) in the plasma, bile, intestinal contents, and liver tissue of Sprague-Dawley rats after intravenous and oral administration of ursodeoxycholic acid (UDCA). Infusion of [2,2,4,4-2H4]UDCA confirmed delta 22-UDCA to be a specific metabolite of UDCA. Definitive confirmation of this unique and major metabolite was established by liquid secondary ionization mass spectrometry and gas chromatography-mass spectrometry by comparison of the retention index and mass spectrum with an authentic standard of delta 22-UDCA. When rats were fed a diet containing 1.0% UDCA, high concentrations of delta 22-UDCA were found in the plasma (40.3 +/- 11.8 mumol/L) and liver tissue (300.9 +/- 64.2 nmol/g of tissue), and these represented 36% and 57%, respectively, of the UDCA concentration. In animals fed 0.4% and 1.0% UDCA, the mass of delta 22-UDCA in the jejunum was high (7.5 +/- 0.9 and 6.6 +/- 0.6 mg, respectively), accounting for 50-60% of the total UDCA, but diminished markedly along the intestine, accounting for < 3% of the total UDCA in the colon. Although delta 22-UDCA was not found in biological samples from control rats, delta 22-beta-muricholic and delta 22-omega-muricholic acids were normal constituents of plasma and intestinal contents and were major muricholate isomers in liver tissue and bile. Synthesis of delta 22-bile acids appears to be highly specific toward bile acids possessing a functional 7 beta-hydroxyl group. We presume that, in common with pathways for endogenous bile acid synthesis, partial side-chain oxidation of UDCA occurs in the peroxisome with formation of alpha/beta unsaturation; since UDCA has only a 5-carbon side chain, release of propionic or acetic acid is not possible, beta-oxidation proceeds no further, and delta 22-UDCA is formed. While the mechanism of formation and physiological significance of delta 22-bile acids remain to be established, our data indicate that partial beta-oxidation is a quantitatively important pathway for endogenous bile acid synthesis and for UDCA metabolism in this species.

Reduction of urinary bile alcohol excretion and serum cholestanol in patients with cerebrotendinous xanthomatosis after oral administration of deoxycholic acid

Deoxycholic acid and chenodeoxycholic acid were administered alternately to four patients with cerebrotendinous xanthomatosis. During this oral therapy serum cholestanol and urinary bile alcohols were determined. Both showed a marked decrease after the start of the two different therapies. It can be concluded that not only chenodeoxycholic acid but also deoxycholic acid is able to suppress endogenous human bile acid synthesis, which is in accordance with other experiments describing the effect of feeding of various bile acids on endogenous bile acid synthesis.

Transport, metabolism, and effect of chronic feeding of lagodeoxycholic acid: A new, natural bile acid

Ursodeoxycholic acid, the 7β-hydroxy epimer of chenodeoxycholic acid, is more hydrophilic and less hepatotoxic than chenodeoxycholic acid. Because “lagodeoxycholic acid,” the 12β-hydroxy epimer of deoxycholic acid, is also more hydrophilic than deoxycholic acid, it was hypothesized that it should also be less hepatotoxic than deoxycholic acid. To test this, lagodeoxycholic acid was synthesized, and its transport and metabolism were examined in the rat, rabbit, and hamster. The taurine conjugate of lagodeoxycholic acid was moderately well transported by the perfused rat ileum (Tmax = 2 μmol/ min · kg). In rats and hamsters with biliary fistulas, the taurine conjugate of lagodeoxycholic acid was well transported by the liver with a Tmax > 20 μmol/ min · kg; for the taurine conjugate of deoxycholic acid, doses infused at a rate >2.5 μmol/min · kg are known to cause cholestasis and death. Hepatic biotransformation of lagodeoxycholic acid in the rabbit was limited to conjugation with glycine; in the hamster, lagodeoxycholic acid was conjugated with glycine or taurine; in addition, 7-hydroxylation occurred to a slight extent (~10%). When lagodeoxycholic acid was instilled in the rabbit colon, it was absorbed as such although within hours it was progressively epimerized by bacteria to deoxycholic acid. When injected intravenously and allowed to circulate enterohepatically, lagodeoxycholic acid was largely epimerized to deoxycholic acid in 24 hours. Surgical creation of a distal ileostomy abolished epimerization in the rabbit, indicating that exposure to colonic bacterial enzymes was required for the epimerization. Lagodeoxycholic acid was administered for 3 weeks at a dose of 180 μmol/day (0.1% by weight of a chow diet; 2–4 times the endogenous bile acid synthesis rate); other groups received identical doses of deoxycholic acid (hamster) or cholyltaurine, a known precursor of deoxycholic acid (rabbit). After 3 weeks of lagodeoxycholic acid ingestion, liver test results and liver appearance were normal. The total bile acid pool expanded by 37% in the rabbit, lagodeoxycholic acid composing 10% of biliary bile acids. In the hamster, the total bile acid pool was expanded by 95%, lagodeoxycholic acid composing 22% of biliary bile acids; biliary lipid secretion remained unchanged. Tracer studies indicated that the fractional turnover rate of lagodeoxycholic acid was high (157%/day, rabbit; 116%/day, hamster) because of its rapid epimerization to deoxycholic acid in the colon. These studies indicate that lagodeoxycholic acid, the more hydrophilic epimer of deoxycholic acid, is transported and metabolized as other dihydroxy bile acids but is much less toxic than deoxycholic acid. Because of its rapid bacterial epimerization to deoxycholic acid, it shows only modest accumulation in circulating bile acids when ingested chronically by rabbits or hamsters at low doses.

Bile acid synthesis: down-regulation by monohydroxy bile acids.

The regulation of bile acid synthesis was studied in rabbits after interruption of the enterohepatic circulation by choledochoureteral anastomosis. Total daily bile acid output was 772 +/- 130 (SD) mumol/24 h, of which greater than 95% was glycocholic acid. Administration of deoxycholic or cholic acid or their conjugates (300-800 mumol) or gall-bladder bile failed to down-regulate endogenous bile acid synthesis. In contrast, chenodeoxycholic acid administration did down-regulate bile acid synthesis, but this effect was related to the formation and excretion of lithocholic acid. This observation was confirmed by the finding that i.v. infusion of 10-20 mumol of either lithocholic acid or 3 beta-hydroxy-5-cholenoic acid significantly reduced cholic acid synthesis. Thus monohydroxy bile acids, derived from either hepatic or intestinal sources, participate in the down-regulation of bile acid synthesis.

Detection of carriers of cerebrotendinous xanthomatosis

Patients suffering from cerebrotendinous xanthomatosis (an autosomal recessive inborn error of metabolism) can easily be distinguished from patients not suffering from this disease, as the first excrete large amounts of the bile alcohol, 5β-cholestane -3α, 7α, 12α, 23,25-pentol, in urine, whereas the second do not. In order to find out, whether carriers of cerebrotendinous xanthomatosis can be detected in a biochemical way, we compared known carriers with controls. The urinary excretions of 5β-cholestane-3α, 7α, 12α, 23,25-pentol of both groups were practically absent and no selection of carriers with cerebrotendinous xanthomatosis could be made on that basis. When, however, carriers and non-carriers were subjected to cholestyramine treatment, by which endogenous bile acid synthesis was stimulated, the urinary excretion of 5β-cholestane-3α, 7α, 12α, 23,25-pentol in the carrier rose considerably, whereas this excretion remained essentially the same in the non-carriers. This test can be of value in the genetic counseling of carriers with cerebrotendinous xanthomatosis and helpful in the detection of newborn patients with cerebrotendinous xanthomatosis.

Bile acid therapies applied to patients suffering from cerebrotendinous xanthomatosis

Patients suffering from cerebrotendinous xanthomatosis, an inborn error of metabolism in bile acid synthesis, were given oral treatment with chenodeoxycholic acid, ursodeoxycholic acid, cholic acid and taurocholic acid. The effectiveness of the different therapies was evaluated by measuring the urinary excretion of 5β-cholestane-3α, 7α,12α,23,25-pentol, which should decrease, when the administered bile acid is able to suppress endogenous bile acid synthesis. From the results it is concluded that chenodeoxycholic acid and cholic acid activate the bile acid negative feedback mechanism, contrary to ursodeoxycholic acid and taurine conjugated cholic acid. Either cholic acid or chenodeoxycholic acid are the therapies of choice for the treatment of cerebrotendinous xanthomatosis. For various reasons the use of cholic acid is especially recommended.

Effect of ursodeoxycholate and its taurine conjugate on bile acid synthesis and cholesterol absorption

Six male subjects with normal gastroenterologic function were studied to determine the effects of ursodeoxycholic (15 mg/kg · day) and tauroursodeoxycholic (20 mg/kg · day) acid feeding on bile acid synthesis and cholesterol absorption. Each bile acid was fed for 1 mo and withheld for the next month. Subjects remained on a metabolic ward and consumed a constant diet of 500 mg of cholesterol mixed with solid and liquid formulas. Before the study started, each subject received 50 μCi of [4-14C]cholesterol intravenously. During the study, stools were collected for the determination of 24-h fecal acidic and neutral sterol excretion, and blood was drawn twice weekly for determination of serum cholesterol specific activity. At the end of each month an intestinal perfusion study was performed to measure total bile acid pool size and hourly biliary secretion rates of cholesterol, phospholipid, and bile acid. From these data, the percentage of cholesterol absorption and total endogenous bile acid synthesis could be calculated. Neither ursodeoxycholic nor tauroursodeoxycholic acid feeding decreased endogenous bile acid synthesis. During bile acid feeding periods, the percentage of cholesterol absorption was decreased.

Differing effects of ursodeoxycholic or chenodeoxycholic acid on biliary cholesterol saturation and bile acid metabolism in man. A dose-response study.

A dose-response study comparing ursodeoxycholic and chenodeoxycholic acid was carried out in six men with asymptomatic radiolucent gallstones present in well-visualizing gallbladders. The study tested the effects of a low (averaging 6 mg/kg/day) or medium dose (averaging 11 mg/kg/day) of each bile acid on the cholesterol saturation of bile as well as on bile acid metabolism, as inferred from biliary and fecal bile acid composition. Ursodeoxycholic acid, at low or medium doses, induced bile desaturation in most patients, whereas chenodeoxycholic acid did not. Despite the greater desaturation efficacy of ursodeoxycholic acid, biliary bile acids became less enriched with the administered bile acid during ursodeoxycholic acid treatment than during chenodeoxycholic acid treatment. Both bile acids were nearly completely 7-dehydroxylated to lithocholic acid by colonic bacteria, but biliary lithocholic increased only slightly (and similarly) with each bile acid. Fecal bile acid composition suggested that administered ursodeoxycholic acid suppressed endogenous bile acid synthesis much less than chenodeoxycholic acid. The results indicate that ursodeoxycholic acid and chenodeoxycholic acid have similar but not identical effects on bile acid metabolism, but that for a given dose, ursodeoxycholic acid is a more potent desaturating agent than chenodeoxycholic acid. The results suggest that cholesterol gallstone dissolution with ursodeoxycholic acid should occur with a dose of 8-10 mg/kg in most nonobese patients.