Modified Bile Acids Research Articles

P1137 : Integrated efficacy summary for obeticholic acid in subjects with primary biliary cirrhosis

Background and Aims: Obeticholic acid (OCA), a modified bile acid and farnesoid x receptor (FXR) agonist, is currently in late-phase development for the treatment of primary biliary cirrhosis (PBC), a rare cholestatic liver disease. In two Phase 2 trials (3 months) and in the Phase 3 POISE trial (12 months) 5mg to 50mg OCA, once daily as monotherapy or add-on to UDCA, produced significant improvements in markers of cholestasis and inflammation. The objective of this integrated analysis was to evaluate the efficacy of ≤10mg OCA, the proposed indicated doses for the treatment of PBC, as monotherapy or in combination with UDCA in an integrated fashion across the 3 trials compared to placebo. Methods: Individual subject data from 3 completed, randomized, controlled double-blind trials of OCA once daily were pooled for this analysis (OCA ≤10mg N=201; placebo N=134; OCA 25mg N=48; OCA 50mg N=57). All placebo subjects were pooled as were OCA doses of 5mg, titration from 5 to 10mg, and 10mg (≤10mg OCA). Inclusion criteria included ALP ≥1.67×ULN or total bilirubin >ULN but <2×ULN. Analyses were repeated based on baseline concomitant UDCA use. Efficacy was evaluated using a composite endpoint shown to correlate with long-term survival (ALP <1.67 ULN with a minimum 15% reduction and a normal bilirubin) (Lammers 2014) and assessment of liver biochemistry and inflammation. Results: Baseline characteristics were generally similar between treatment groups. Baseline ALP was higher in monotherapy subjects compared to UDCA combination subjects. Efficacy data are presented in the Table. At the end of double blind treatment significantly more OCA-treated subjects achieved the composite endpoint compared to placebo when used as monotherapy or in combination with UDCA. OCA treatment was associated with statistically significant and clinically meaningful decreases in ALP as well as GGT, ALT, and AST. While the subjects in the monotherapy group had higher ALP at baseline than the OCA plus UDCA group, the two groups reached similar ALP levels by the end of the double-blind period. Pruritus was the most common adverse event associated with PBC and showed a dose-related increase in incidence with OCA.

Role of Endothelin 3 (ET3) in Estradiol 17B‐glucuronide (E217G)‐induced Cholestasis in the Rat

We previously reported that ET3 induces choleresis through ETB receptors coupled to nitric oxide (NO). It enhances, independently of hemodynamic changes, bile acid dependent and independent bile flows and promotes plasma membrane insertion of the main hepatic transporters involved in bile genesis and increases their mRNA expression (Clin Sci., 125:531, 2013). In this work we aimed to determine whether ET3 played a beneficial role in E217G‐induced cholestasis. Sprague‐Dawley rats were infused with ET3 (5 ng/kg/min) or vehicle for 30 min followed by E217G administration to induce cholestasis. Bile samples were collected every 5 min for 120 min. Bile acids were assessed in bile by capillary electrophoresis. Other set of animals were also pretreated with L‐NAME (NO synthases inhibitor) or BQ788 (ETB receptor antagonist) before ET3 and E217G administration. ET3 prevented E217G‐induced cholestasis and the response was abolished by BQ788 or L‐NAME. Furthermore ET3 also modified bile acid excretion, particularly ursodeoxycholic acid and lithocholic acid as compared with control and E217G. ET3 induced no changes in plasma transaminases, bilirubin, alkaline phosphatase or 5´nucleotidase or in the hepatic histology assessed by light microscopy in stained hematoxylin and eosin liver samples. Present findings show that ET3 through ETB receptors coupled to NO prevents E217G‐induced cholestasis and modifies bile acid profile excretion in the rat. Results further suggest that the ETB receptor may represent a promising therapeutic target in pathophysiological situations where bile flow is impaired.

Physical Activity as a Determinant of Fecal Bile Acid Levels

Physical activity is protective against colon cancer, whereas colonic bile acid exposure is a suspected risk factor. Although likely related, the association between physical activity and bile acid levels has not been well-studied. Furthermore, the effect of triglycerides, which are known to modify bile acid levels, on this relationship has not been investigated. We conducted a cross-sectional analysis of baseline fecal bile acid levels for 735 colorectal adenoma formers obtained from participants in a phase III ursodeoxycholic acid chemoprevention trial. Compared with the lowest quartile of recreational physical activity duration, the highest quartile was associated with a 17% lower fecal bile acid concentration, adjusted for age, sex, dietary fiber intake, and body mass index (P = 0.042). Furthermore, consistent with a previously established relationship between serum triglyceride levels and bile acid metabolism, we stratified by triglyceride level and observed a 34% lower fecal bile acid concentration (highest versus lowest quartiles of physical activity) in individuals with low triglycerides (<136 mg/dL; P = 0.002). In contrast, no association between physical activity and fecal bile acid concentration was observed for subjects with high triglycerides (> or =136 mg/dL). Our results suggest that the biological mechanism responsible for the protective effect of physical activity on the incidence of colon cancer may be partially mediated by decreasing colonic bile acid exposure. However, this effect may be limited to individuals with lower triglyceride levels.

Immunonutrients and the Critically Ill Neonate

After completing this article, readers should be able to: 1. List the otherwise “nonessential” nutrients that may be required by the critically ill neonate. 2. Explain why omega-3 fatty acids do not cause as much inflammation as their omega-6 counterparts. 3. Define pre- and probiotics and describe how they can prevent colonization of the intestine by pathogenic organisms. 4. Describe the potential protective effects of lactoferrin on the neonatal gastrointestinal tract. In a critically ill individual, the intestinal barrier becomes compromised because of stress, lack of enteral feedings, and ischemic-reperfusion injury. In the preterm neonate, the mucosal barrier is not fully functional (see article on innate immunity in this issue of NeoReviews ). The combination of a damaged and immature gut barrier may lead to increased intestinal permeability, aberrant antigen transfer, and immune response, which can explain the vulnerability to infection, inflammation, and hypersensitivity at an early age. In patients dying of sepsis, there is clear evidence of an imbalance in pro- and anti-inflammatory cytokine production, a failure to maintain antioxidant defenses, and high levels of activation of nuclear factor- kappa-B (NF-kappa-B). Over the past several years, it has become more evident that the proinflammatory cytokine response, as part of an uncontrolled systemic inflammatory response syndrome (SIRS), plays an integral role in premature labor, chronic lung disease, cerebral palsy, necrotizing enterocolitis (NEC), and sepsis. Because the gut is a primary origin of SIRS, it is reasonable to suggest that nutritional agents might stabilize the intestinal mocosal barrier, alter the balance of pro- and anti- inflammatory cytokines, and prevent excessive activation of NF-kappa-B or other signaling pathways. Some nutrients, such as glutamine, arginine, omega-3 fatty acids, nucleotides, and probiotics, have been shown to have a considerable influence on immune function (eg, delayed hypersensitivity, lymphocyte subpopulation counts, immunologic test) and improve metabolic and nutritional indices such as …

Synthetic Bile Acids: Novel Mediators of Apoptosis

Summary and implications In this paper, we outlined the current understanding of naturaland synthetic bile acid signaling in apoptosis. Much insightwas gained in recent years, particularly with respect to theinducers of the hydrophobic bile acid signaling cascade.Moreover, the newly synthesized bile acids also inducedapoptosis in several human cancer cells, which were notderived from hepatocytes, cholangiocytes, and ilealenterocytes. Therefore, the new synthetic bile acids might beapplicable novel apoptosis mediators for the treatment ofvarious cancer cells.In human breast and prostate cancer cells with differenttumor suppressor p53 status, the synthetic bile acid derivative-induced growth inhibition and apoptosis were associated withthe up-regulation of Bax and p21 WAF1/CIP1 , and the effects weremediated via a p53-inpendent pathway. In Jurkat human T cellleukemia, the synthetic bile acid derivatives induced apoptosisthrough caspase activation. Additionly, the synthetic bile acidsinduced apoptosis in a JNK dependent manner in SiHa humancervical cancer cells, PC3 prostate cancer cells, HT29 coloncancer cells, and TE671 brain tumor cells (Im, E.O., Yoo,Y.H., and Kim, N.D., unpublished data).Alterations in cell survival play a critical role for thepathogenesis of various human diseases, including cancer(Thompson, 1995). Administration of modified bile acids thatinduce apoptosis might represent a rational therapy for tumorsthat originate from several different types of cells. Therefore,these novel derivatives of bile acids may represent promisingchemical entities, which specifically target various cancercells by triggering apoptosis. These could be important leadcompounds for the development of new anticancer agents thatare based on the structure of bile acids.Acknowledgments This work was supported by grant No.R01-2001-00145 from the Korea Science & EngineeringFoundation and by a Pusan National University ResearchGrant.

Modified bile acid profiles in mixed neutron and gamma-irradiated pigs

Purpose:To determine the effect of mixed neutron and gamma irradiation on the bile acid pool, which may be a key factor in radiation-induced diarrhoea. Materials and methods:The bile duct of pigs was catheterized to derive bile over several experimental weeks, both before and after a 5.9Gy neutron and gamma-irradiation. After measurement of the volume and sampling, bile was returned to the pig via a duodenal catheter. Samples of bile were analysed by HPLC for their individual and total bile acid content. Blood samples were also collected for total bile acid determination. Results:Bile flow was significantly decreased during the first 24h and after the fifth day post-irradiation. Whereas total bile acid concentration in bile was not altered, profiles of individual bile acids were significantly altered as early as the first post-irradiation day. Such modifications in these profiles resulted in a change of the properties of the bile acid pool. An increased proportion of dihydroxylated bile acids known to be more deleterious for the intestine was observed. Conclusions:Neutron and gamma-irradiation leads to modifications of bile acid profiles, which may partly explain radiation-induced diarrhoea by a coherent physiopathological mechanism.

Modified bile acids as carriers for peptides and drugs

For the development of future drugs two aspects are of major importance, a site-specific drug action without adverse side-effects and a preferably oral applicability. The liver has a central role in drug action and many disorders are unique to the liver demanding a liver-specific drug action. In oral drug therapy the small intestine is often the limiting barrier of drug absorption. Bile acids are natural substrates undergoing an enterohepatic circulation involving the liver and the small intestine. This organotropism of bile acids is achieved by specific Na+-dependent transport systems in the plasma membrane of hepatocytes and ileocytes. Di- and tripeptides as well as orally active α-amino-β-lactam antibiotics are intestinally absorbed by a H+/oligopeptide cotransport system of high transport capacity. We, therefore, investigated whether the hepatic and the intestinal bile acid transport systems as well as the intestinal H+/oligopeptide transporter can be used in drug therapy to improve the membrane permeability and intestinal absorption of peptide drugs, to target a drug to the liver and the biliary system and to obtain liver-specific drugs. For this, modified bile acids with linkers of varying structure, length, position and stereochemistry at the steroid nucleus were synthesized and covalently linked to drugs or peptides or alternatively bile acid structural elements were introduced into drugs. To investigate the H+/oligopeptide transporter as a putative peptide delivery system, peptides were covalently attached to the 3′-position of the tripeptide-analogue d-cephalexin. The interaction of these bile acid and cephalexin conjugates with the hepatic and intestinal bile acid and peptide transport systems as well as their pharmacokinetic and pharmacodynamic behaviour was investigated by transport measurements and photoaffinity labeling techniques using membrane vesicles, isolated hepatocytes and in vivo models.

Intestinal absorption of peptides by coupling to bile acids.

Poor intestinal absorption of peptides greatly limits their use as drugs for the treatment of chronic diseases. Since bile acids are efficiently absorbed by an active, Na(+)-dependent transport system in the ileum of mammals, model peptides of different chain length were attached to the 3-position of modified 3 beta-(omega-amino-alkoxy)-7 alpha, 12 alpha-dihydroxy-5 beta-cholan-24-oic acid. These peptide-bile acid conjugates inhibited Na(+)-dependent [3H]taurocholate uptake into brush-border membrane vesicles isolated from rabbit ileum in a concentration-dependent manner. Furthermore, photoaffinity labeling of the bile acid-binding proteins of M(r) 93,000 and 14,000, identified as the protein components of the ileal Na(+)-dependent bile acid transport system in rabbit ileum (Kramer, W., Girbig, F., Gutjahr, U., Kowalewski, S., Jouvenal, K., Müller, G., Tripier, D., and Wess, G. (1993) J. Biol. Chem. 268, 18035-18046) by the photoreactive taurocholate analogue, (3,3-azo-7 alpha, 12 alpha-dihydroxy-5 beta [7 beta, -12 beta-3H]cholan-24-oyl)-2-aminoethanesulfonic acid, was inhibited by the peptide-bile acid conjugates. In contrast, the parent peptides and amino acids neither had a significant effect on [3H]taurocholate uptake by ileal brush-border membrane vesicles nor on photoaffinity labeling of the ileal bile acid-binding membrane proteins. The inhibitory effect of peptide-bile acid conjugates on [3H]taurocholate transport and photoaffinity labeling of the bile acid-binding proteins in rabbit ileal vesicles decreased with increasing chain length of the attached peptide radical. By in vivo ileum perfusion in anesthetized rats an intestinal absorption of the bile acid conjugate S3744 of the fluorescent oxaprolylpeptide 4-nitrobenzo-2-oxa-1,3-diazol-beta-Ala-Phe-5-Opr-Gly (S1037) and secretion of the intact compound into bile could be demonstrated, whereas the parent peptide S1037 or its t-butylester S4404 were not absorbed. The intestinal absorption of S3744 showed a similar temperature dependence as [3H]taurocholate absorption and was inhibited by the presence of taurocholate indicating a carrier-mediated uptake of S3744 via the ileal bile acid transporter. In conclusion, these results indicate that oligopeptides can be made enterally absorable by coupling to modified bile acid molecules making use of the specific intestinal absorption pathway for bile acids. This finding may be of great importance for the design and development of orally active peptide drugs.

Effects of Different Formula Feeds on the Developmental Pattern of Urinary Bile Acid Excretion in Infants

Summary:The excretion of bile acids in urine was followed prospectively during the first year of life in 17 infants fed different diets from the age of 3 to 10 days. Eight infants were breast‐fed, four were fed formulas that were based on adapted cow's milk, and five were fed a formula that was based on soy protein isolate. The formulas had higher protein concentrations than human milk; had different types of proteins, and had not been supplemented with taurine. Urinary bile acids were determined by gas‐liquid chromatographic/mass spectrometric analyses of 24‐h urinary samples collected at 1–12 days (only formula‐fed infants) and at 1, 3, 6, 9, and 12 months of age. The results showed a higher urinary bile acid excretion at 3 months of age in both formula groups than in the breastfed infants. A deficiency of dietary taurine during formula‐feeding did not seem to limit the formation of taurine conjugates during the first month of life. The developmental pattern of urinary bile acid excretion during the first year differed according to the type of feeding. Isomers of cholic and chenodeoxycholic acid appeared in the urine of all breast‐fed infants at 6 to 12 months of age. These metabolites, assumed to be the first metabolites derived from the developing gut flora of the infants, appeared at an earlier age and in higher amounts in both formula groups compared to breast‐fed infants. Bile acids lacking a 7‐hydroxy group, known to be formed by the intestinal flora, appeared in infants in all feeding groups later than the isomers. The results of the study imply that the early introduction of formula may modify bile acid metabolism in infants.

Drug targeting to the liver with bile acids: THE “trojan horse” resurrected?

Bile acids are selectively taken up from portal blood into the liver by specific transport systems in the hepatocyte plasma membrane. Therefore, studies were performed to evaluate the potential of bile acids as shuttles to deliver drugs specifically to the liver. The alkylating cytostatic drug chlorambucii and the fluorescent prolyl-4-hydroxylase inhibitor 4-nitrobenzo-2-oxa-1,3-diazol-β-Ala-Phe-5-oxaproline-Gly were covalently linked via an amide bond to 7α, 12α,-dihydroxy-3β-(ω-aminoalkoxy)-5-β-cholan-24-oic acid. The chlorambucil-bile acid conjugates S 2521, S 2539, S 2567, and S 2576 inhibited Na+-dependent [3H]taurocholate uptake in a concentration-dependent manner both into isolated rat hepatocytes and rabbit ileal brush border membrane vesicles, whereas the parent drug chlorambucil showed no significant inhibitory effect. The chlorambucil-bile acid conjugates were able to prevent photoaffinity labeling of bile acid binding proteins in rat hepatocytes by the photolabile [3H]7,7-azo derivative of taurocholic acid indicating their bile acid character. The chlorambucil-bile acid conjugate S 2577 was able to alkylate proteins demonstrating the drug character conserved in the hybridmolecules. Liver perfusion experiments revealed a secretion profile of the chlorambucil-bile acid conjugate S 2576 into bile very similar to taurocholate compared to chlorambucil which is predominantly excreted by the kidney. 4-Nitrobenzo-2-oxa-1,3-diazol-β-Ala-Phe-5-oxaproline-Gly-t-butylester (S 4404), a fluorescent peptide inhibitor of prolyl-4-hydroxylase, was not transported in intact form from portal blood into bile in contrast to its bile acid conjugate S 3744; about 25% of the peptide-bile acid conjugate S 3744 was secreted in intact form into bile within 40 min compared with less than 4% of the parent oxaprolylpeptide S 4404. In conclusion, these studies reveal that modified bile acid molecules can be used as “Trojan horses” to deliver a drug molecule specifically into the liver and the biliary system. This offers important pharmacological options for the development of liver-specific drugs. This study was designed to determine whether the conjugation product of L-T3 with cholic acid would result in a liver-targeted compound (CGH 509A) with hypocholesterolemic (HC) activity significantly dissociable from cardiovascular (CV) and thyroxine-suppressing (TS) effects normally observed with thyroid hormone. Evaluation of HC activity in lipemic rats showed that CGH 509A was 6 times less potent than L-T3 with ED25 values estimated at 150 and 25 nmol/kg, respectively. CV function measured as changes in atrial rate, atrial tension and heart weight was determined in euthyroid rats. CGH 509A was at least 64 times less cardio-stimulant than L-T3, with minimum effective doses estimated at 2350 and 37 nmol/kg, respectively. TS activity was assessed in euthyroid rats as the potency of any compound to reduce plasma T4 levels. CGH 509A was 50 times less potent than L-T3 with ED50 values estimated at 900 and 18 nmol/kg, respectively. From these results, it is clear that, while L-T3 was equally potent on HC, CV and TS activities, the HC potency of CGH 509A was at least 15 and 6 times greater than its CV and TS potencies, respectively.

Liver-specific drug targeting by coupling to bile acids.

Bile acids are selectively taken up from portal blood into the liver by specific transport systems in the hepatocyte plasma membrane. Therefore, studies were performed to evaluate the potential of bile acids as shuttles to deliver drugs specifically to the liver. The alkylating cytostatic drug chlorambucil and the fluorescent prolyl-4-hydroxylase inhibitor 4-nitrobenzo-2-oxa-1,3-diazol-beta-Ala-Phe-5-oxaproline-Gly were covalently linked via an amide bond to 7 alpha, 12 alpha,-dihydroxy-3 beta- (omega-aminoalkoxy)-5-beta-cholan-24-oic acid. The chlorambucil-bile acid conjugates S 2521, S 2539, S 2567, and S 2576 inhibited Na(+)-dependent [3H]taurocholate uptake in a concentration-dependent manner both into isolated rat hepatocytes and rabbit ileal brush border membrane vesicles, whereas the parent drug chlorambucil showed no significant inhibitory effect. The chlorambucil-bile acid conjugates were able to prevent photoaffinity labeling of bile acid binding proteins in rat hepatocytes by the photolabile [3H]7,7-azo derivative of taurocholic acid indicating their bile acid character. The chlorambucil-bile acid conjugate S 2577 was able to alkylate proteins demonstrating the drug character conserved in the hybrid-molecules. Liver perfusion experiments revealed a secretion profile of the chlorambucil-bile acid conjugate S 2576 into bile very similar to taurocholate compared to chlorambucil which is predominantly excreted by the kidney. 4-Nitrobenzo-2-oxa-1,3-diazol-beta-Ala-Phe-5-oxaproline-Gly- t-butylester (S 4404), a fluorescent peptide inhibitor of prolyl-4-hydroxylase, was not transported in intact form from portal blood into bile in contrast to its bile acid conjugate S 3744; about 25% of the peptide-bile acid conjugate S 3744 was secreted in intact form into bile within 40 min compared with less than 4% of the parent oxaprolylpeptide S 4404. In conclusion, these studies reveal that modified bile acid molecules can be used as "Trojan horses" to deliver a drug molecule specifically into the liver and the biliary system. This offers important pharmacological options for the development of liver-specific drugs.

Modified bile acids: preparation of 7α,12α-dihydroxy-3β- and 7α,12α-dihydroxy-3α-(2-hydroxyethoxy)-5β-cholanic acid and their biological activity

Methodology for the preparation of 7α-12α-dihydroxy-3β- (2) and 7α,12α-dihydroxy-3α-(2-hydroxyethoxy)-5β-cholanic acid (3) is described. Nucleophilic displacement of the 3-mesylate of unprotected cholic acid with ethylene glycol led to the 3β-isomer whereas the 3α-isomer was synthesized via the 7,12-diacetyl protected 3-allyl ether of methyl cholate. Only the 3α-isomer 3 is recognized by the ileal bile acid transport system with affinity comparable to cholic acid.

Effect of natural and structurally modified bile acids on cholesterol metabolizing enzymes in rat liver microsomes. II

The effect of unsodeoxycholic acid analogues bearing modifications at the side-chain moiety of the molecule was tested on cholesterol 7α-hydroxylase and HMG-CoA reductase in rat liver microsomes. The compounds included 23 R,S mixture and the single isomers 23 R and 23 S of 23 methylursodeoxycholic acid (23-methyl UDCA), the isomeric mixture ( cis + trans) of 3α,7β-dihydroxy-20,22-methylen-5β-cholan-23-oic acid (norcypro-UDCA) and the corresponding single isomers. Each steroid was added to liver microsomes as the sodium salt, at concentrations ranging from 25 to 200 μM. Isomers 23 R and 23 S of 23-methyl-UDCA inhibited cholesterol 7α-hydroxylase in a concentration-dependent manner. The inhibitory capacity was similar for the two isomers. The extent of inhibition of the analogues was greater than that of the parent compound UDCA. Shortening of the side-chain in norcypro-UDCA resulted in a partial loss of the inhibitory effect, as compared to cypro-UDCA (3α,7β-dihydroxy-22,23-methylen-5β-cholan-24-oic acid). None of these bile acid derivatives affected the activity of the enzyme HMG-CoA reductase.

Contrasting effects of water‐soluble and water‐insoluble dietary fibers on bile acid conjugation and taurine metabolism in the rat

The effect of the type of dietary fiber on the bile acid and taurine metabolism was examined in rats. Diets containing 10% of various water-soluble fibers (citrus pectin, konjak mannan, guar gum) as compared to a fiber-free diet increased biliary excretion of total bile acids. In contrast, water-insoluble dietary fibers (cellulose, corn bran, chitin; 10% in the diets) as well as cholestyramine (5% in the diet) considerably decreased bile acid excretion. Water-soluble dietary fiber-mediated increases in bile acid excretion were totally attributable to increases in glycine-conjugates. Thus, these fibers greatly increased the bile acid glycine-to-taurine ratio (G/T). Excretion of glycine conjugates decreased more than that of taurine conjugates in rats fed various water-insoluble dietary fibers. As a result, G/T in rats fed water-insoluble fibers was significantly lowered as compared to G/T in animals fed a fiber-free diet. Cholestyramine did not affect the G/T ratio of bile acids. Fecal bile acid excretion and the activities of hepatic cholesterol 7 alpha-hydroxylase (EC 1.14.13.17) in rats fed various water-soluble dietary fibers approximately doubled as compared to the respective values for rats fed a fiber-free diet. Whereas cholestyramine greatly increased these parameters, water-insoluble fibers did not significantly affect them. Various water-soluble fibers decreased hepatic concentration and urinary excretion of taurine as well as the activity of hepatic cysteine dioxygenase (EC 1.13.11.20). In contrast, water-insoluble fibers considerably increased hepatic taurine concentrations and enzyme activities. The parameters for taurine metabolism were unaffected by cholestyramine. It was suggested that the types of dietary fiber affected hepatic taurine synthesis and thus modified bile acid glycine/taurine ratios.

Effect of natural and structurally modified bile acids on cholesterol metabolizing enzymes in rat liver microsomes

The effect of chenodeoxycholic (CDCA), ursodeoxycholic (UDCA), tauroursodeoxycholic (TUDCA), cholic (CA), ursocholic (UCA) acids, analogues of CDCA and UDCA with a cyclopropyl ring at C 22, C 23 (cypro-CDCA and cypro-UDCA) and 23-methylursodeoxycholic acid (MUDCA) on cholesterol 7α-hydroxylase was studied in rat liver microsomes. Cypro-analogues consisted of a mixture of four diasteroisomers, while MUDCA was the racemic mixture of two enantiomers. Each steroid was added to liver microsomes at concentrations ranging from 10 to 200 μM. With the exception of UCA and CA, all the bile acids inhibited cholesterol 7α-hydroxylase activity. The inhibition shown by cypro-CDCA and cypro-UDCA was stronger than that observed with the corresponding natural compounds. 22 S,23 S cypro-UDCA exhibited an inhibitory effect which was more pronounced than that of the diasteroisomer mixture. The isomer 22 R,23 S was less effective and decreased cholesterol 7α-hydroxylase activity in a manner comparable to that of UDCA. The effect of CDCA, UDCA and the cyclopropyl analogues was also tested with respect to HMG-CoA reductase and acylCoA cholesterol acyltransferase (ACAT) activities. ACAT was stimulated by the isomer 22 S,23 S cypro-UDCA but not affected by the other bile acids. No effect was observed as regards HMG-CoA reductase.

The role of bile acids in colonic carcinogenesis.

Several line of evidence suggest that bile acids may be implicated in the pathogenesis of colonic cancer. A high consumption of fat and animal protein and a low dietary intake of fiber have been shown to be related to the incidence of colonic cancer. From these epidemiologic observations the hypothesis was proposed that the correlation between diet and colon cancer might be explained by the involvement of bile acids. Populations at a high risk of developing cancer were shown to have an increased excretion both of total and bacterially modified bile acids in their feces. Animal studies demonstrated a cocarcinogenic effect of bile acids and experimental diets containing large amounts of fat did not only induce an increased bile acid excretion but also an enhanced tumor formation in the colon. Furthermore, microbial in vitro tests showed a comutagenic activity of secondary bile acids. However, case control studies comparing the fecal bile acid excretion pattern in colonic cancer patients and control subjects failed to show such a clear relationship, which might be explained by rather similar dietary habits within one population and individual differences in sensitivity to environmental factors contributing to the tumor development. Cholecystectomy, leading to an increased exposure of bile acids to the intestinal microflora, has been suggested as a predisposing factor for the development of colonic cancer, but the results of experimental and epidemiologic studies so far are rather inconsistent.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Hypolipidemic Drugs on Bile Acid Metabolism in Man

Publisher Summary This chapter discusses the effects of hypolipidemic drugs on bile acid metabolism in man. Hypolipidemic drugs can be classified as either absorbable or unabsorbable. These latter compounds pass through the intestinal tract more or less unchanged and interfere with the absorption of either bile acids or cholesterol. The exact mechansim of the hypolipidemic action of absorbable agents, for example, clofibrate, nicotinic acid, thyroid hormones, and probucol, is less clear than that of unabsorbable drugs. Some of them apparently inhibit hepatic triglyceride and/or very-low-density lipoprotein synthesis and/or release, while others may stimulate removal of lipoproteins from the blood or interfere directly with cholesterol synthesis. The modified lipoprotein metabolism can be associated with changes in synthesis and turnover of cholesterol and subsequently with a modified bile acid metabolism. The chapter highlights the significance of modified lipoprotein and cholesterol metabolisms caused by the action of absorbable hypolipidemic agents on bile acids and the effect of enhanced bile acid metabolism caused by unabsorbable drugs on lipoprotein and cholesterol metabolism.

Analysis of Fecal Bile Acids and Diet Among the Japanese in Hawaii

Fecal samples of 165 Japanese men in Hawaii, age 43 to 74, were analyzed for bile acid content by their conversion to the methyl ester and the trimethylsilyl ether derivative followed by separation on a gas chromatograph. The arithmetic mean of total bile acids for the 165 specimens was 10.96 mg/g dry weight feces. Each of the following bile acids was detectable in over 77% of the fecal specimens: cholic, deoxycholic, lithocholic, and cholanic acid. The intake of Western foods was not positively correlated with the fecal content of secondary or modified bile acids, even though other workers have observed that these bile acids predominated in persons from Westernized countries. Two of the Japanese foods were negatively correlated with the levels of modified bile acids, which suggested that these foods contributed to a decrease in modified bile acids in fecal specimens. Fecal bile acid measurements appeared to be associated with age, but not with weight, height, or serum cholesterol levels.

Novel marine sterols with modified bile acid side chain from the sea pen [formula omitted

Novel marine sterols with modified bile acid side chain from the sea pen [formula omitted

Effects of High Risk and Low Risk Diets for Colon Carcinogenesis on Fecal Microflora and Steroids in Man

We investigated the effects of a high meat mixed Western diet and a nonmeat diet, representing the dietary pattern of high and low risk areas for colon cancer, respectively, on fecal microflora dn on bile acid and neutral sterol patterns in man. The total anaerobic microflora as well as the count of Bacteroides, Bifidobacterium, Peptococcus, and anaerobic Lactobacillus were significantly higher during the period of consumption of a high meat mixed Western diet comparted with the nonmeat-diet consumption period. The difference in total fecal bile acid excretion was not significant between the two dietary periods. Fecal excretion of microbially modified bile acids and neutral sterols was decreased when subjects eating a high meat diet transferred to a nonmeat diet. These results support the fact that diet plays a modifying role on the composition of intestinal microflora, bile acids, and neutral sterols.