1
|
Ridlon JM, Gaskins HR. Another renaissance for bile acid gastrointestinal microbiology. Nat Rev Gastroenterol Hepatol 2024; 21:348-364. [PMID: 38383804 DOI: 10.1038/s41575-024-00896-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 01/16/2024] [Indexed: 02/23/2024]
Abstract
The field of bile acid microbiology in the gastrointestinal tract is going through a current rebirth after a peak of activity in the late 1970s and early 1980s. This renewed activity is a result of many factors, including the discovery near the turn of the century that bile acids are potent signalling molecules and technological advances in next-generation sequencing, computation, culturomics, gnotobiology, and metabolomics. We describe the current state of the field with particular emphasis on questions that have remained unanswered for many decades in both bile acid synthesis by the host and metabolism by the gut microbiota. Current knowledge of established enzymatic pathways, including bile salt hydrolase, hydroxysteroid dehydrogenases involved in the oxidation and epimerization of bile acid hydroxy groups, the Hylemon-Bjӧrkhem pathway of bile acid C7-dehydroxylation, and the formation of secondary allo-bile acids, is described. We cover aspects of bile acid conjugation and esterification as well as evidence for bile acid C3-dehydroxylation and C12-dehydroxylation that are less well understood but potentially critical for our understanding of bile acid metabolism in the human gut. The physiological consequences of bile acid metabolism for human health, important caveats and cautionary notes on experimental design and interpretation of data reflecting bile acid metabolism are also explored.
Collapse
Affiliation(s)
- Jason M Ridlon
- Department of Animal Sciences, University of Illinois Urbana-Champaign, Urbana, IL, USA.
- Division of Nutritional Sciences, University of Illinois Urbana-Champaign, Urbana, IL, USA.
- Carl R. Woese Institute for Genomic Biology, University of Illinois Urbana-Champaign, Urbana, IL, USA.
- Cancer Center at Illinois, University of Illinois Urbana-Champaign, Urbana, IL, USA.
- Center for Advanced Study, University of Illinois Urbana-Champaign, Urbana, IL, USA.
- Department of Microbiology & Immunology, Virginia Commonwealth University, Richmond, VA, USA.
| | - H Rex Gaskins
- Department of Animal Sciences, University of Illinois Urbana-Champaign, Urbana, IL, USA.
- Division of Nutritional Sciences, University of Illinois Urbana-Champaign, Urbana, IL, USA.
- Carl R. Woese Institute for Genomic Biology, University of Illinois Urbana-Champaign, Urbana, IL, USA.
- Cancer Center at Illinois, University of Illinois Urbana-Champaign, Urbana, IL, USA.
- Department of Biomedical and Translational Sciences, University of Illinois Urbana-Champaign, Urbana, IL, USA.
- Department of Pathobiology, University of Illinois Urbana-Champaign, Urbana, IL, USA.
| |
Collapse
|
2
|
Sato H, Macchiarulo A, Thomas C, Gioiello A, Une M, Hofmann AF, Saladin R, Schoonjans K, Pellicciari R, Auwerx J. Novel potent and selective bile acid derivatives as TGR5 agonists: biological screening, structure-activity relationships, and molecular modeling studies. J Med Chem 2008; 51:1831-41. [PMID: 18307294 DOI: 10.1021/jm7015864] [Citation(s) in RCA: 226] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
TGR5, a metabotropic receptor that is G-protein-coupled to the induction of adenylate cyclase, has been recognized as the molecular link connecting bile acids to the control of energy and glucose homeostasis. With the aim of disclosing novel selective modulators of this receptor and at the same time clarifying the molecular basis of TGR5 activation, we report herein the biological screening of a collection of natural occurring bile acids, bile acid derivatives, and some steroid hormones, which has resulted in the discovery of new potent and selective TGR5 ligands. Biological results of the tested collection of compounds were used to extend the structure-activity relationships of TGR5 agonists and to develop a binary classification model of TGR5 activity. This model in particular could unveil some hidden properties shared by the molecular shape of bile acids and steroid hormones that are relevant to TGR5 activation and may hence be used to address the design of novel selective and potent TGR5 agonists.
Collapse
Affiliation(s)
- Hiroyuki Sato
- Institut de Genetique et de Biologie Moléculaire et Cellulaire, Centre National de la Recherche Scientifique/INSERM/ULP, Illkirch, France
| | | | | | | | | | | | | | | | | | | |
Collapse
|
3
|
Alvarez M, Jover A, Carrazana J, Meijide F, Soto VH, Tato JV. Crystal structure of chenodeoxycholic acid, ursodeoxycholic acid and their two 3beta,7alpha- and 3beta,7beta-dihydroxy epimers. Steroids 2007; 72:535-44. [PMID: 17509630 DOI: 10.1016/j.steroids.2007.03.007] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/27/2006] [Revised: 02/14/2007] [Accepted: 03/08/2007] [Indexed: 11/19/2022]
Abstract
The crystal structures of chenodeoxycholic acid (CDCA), ursodeoxycholic acid (7beta isomer of CDCA) and their other two epimers (3beta,7alpha- and 3beta,7beta-isomers) have been resolved. The four isomers were recrystallized from p-xylene. CDCA crystal is hexagonal P6(5) while the crystals of the other three isomers are orthorhombic (P2(1)2(1)2(1) space group). Only the 3beta,7beta isomer forms an inclusion complex with the solvent with a 1:1 stoichiometry. In all cases, the three hydrogen bond sites (the two hydroxy groups, O3-H and O7-H, and the carboxylic acid group of the side chain, O24bO24a-H) simultaneously act as hydrogen bond donors and acceptors. By considering that O24a is always donor and O24b is always acceptor, the hydrogen bond sequences can be understood on the basis of the interaction between the two hydroxy groups. However the comparison between the four compounds is complicated by the existence of two molecules in the asymmetric unit in the UDCA crystal resulting in that the same hydrogen bond site (for instance O3) can be donor towards two different acceptors (either O7 or O24b). As in the case of the four isomers of deoxycholic acid (Steroids 2004, 69, 379), the other three isomers present a donor-->acceptor sequence, which is O7-->O3 when O3-H is beta and O3-->O7 when O3-H is alpha. The spatial orientation of the carboxylic acid of the side chain is referred to two almost perpendicular planes (defined by (1) the carbon atoms C1/C6-C17/C20 and by (2) the methyl groups C18-C19 and the two carbon atoms to which they are linked, C10 and C13, respectively). Only the side chain of CDCA evidences a positive deviation towards the hydrophobic beta side of the molecule.
Collapse
Affiliation(s)
- M Alvarez
- Departamento de Química Física, Universidade de Santiago, Campus de Lugo, Facultade de Ciencias, 27002 Lugo, Spain
| | | | | | | | | | | |
Collapse
|
4
|
Keely SJ, Scharl MM, Bertelsen LS, Hagey LR, Barrett KE, Hofmann AF. Bile acid-induced secretion in polarized monolayers of T84 colonic epithelial cells: Structure-activity relationships. Am J Physiol Gastrointest Liver Physiol 2007; 292:G290-7. [PMID: 16901996 DOI: 10.1152/ajpgi.00076.2006] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Bile acid epimers and side-chain homologues are present in the human colon. To test whether such bile acids possess secretory activity, cultured T84 colonic epithelial cells were used to quantify the secretory properties of synthetic epimers and homologues of deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA). In our study, chloride secretion was measured as changes in short-circuit current (DeltaI(sc), in microA/cm2) with the use of voltage-clamped monolayers of T84 cells mounted in Ussing chambers. Bile acids were added at 0.5 mM, a concentration that did not alter transepithelial resistance. Data were expressed as peak DeltaI(sc) (means +/- SD). When added bilaterally, DCA stimulated a DeltaI(sc) response of 15.7 +/- 12.5 microA/cm2. The 12beta-OH epimer of DCA was less potent (DeltaI(sc) = 8.0 +/- 1.7 microA/cm2), whereas its 3beta-OH epimer had no effect. CDCA stimulated secretion (DeltaI(sc) = 8.2 +/- 5.5 microA/cm2), whereas both its 7beta-OH and 3beta-OH epimers were inactive, as was lithocholic acid. HomoDCA (1 additional side-chain carbon) was active (DeltaI(sc) = 7.8 +/- 4.8 microA/cm2), whereas norDCA (1 fewer carbon) and dinorDCA (2 fewer carbons) were not. Taurine conjugates of DCA and CDCA stimulated secretion (DeltaI(sc) = 12.3 +/- 7.5 and 8.8 +/- 4.8 microA/cm2, respectively) from the basolateral side but not the apical side. Uptake of taurine conjugates from the basolateral but not the apical side was shown by mass spectrometry. These studies indicate marked structural specificity for bile acid-induced chloride secretion and show that modification of bile acid structure by colonic bacteria modulates the secretory properties of these endogenous secretagogues.
Collapse
Affiliation(s)
- Stephen J Keely
- Division of Gastroenterology, Department of Medicine, University of California, San Diego, California, USA.
| | | | | | | | | | | |
Collapse
|
5
|
Jover A, Meijide F, Soto VH, Vázquez Tato J, Núñez ER, Ton-Nu HT, Hofmann AF. Successful prediction of the hydrogen bond network of the 3-oxo-12alpha-hydroxy-5beta-cholan-24-oic acid crystal from resolution of the crystal structure of deoxycholic acid and its three 3,12-dihydroxy epimers. Steroids 2004; 69:379-88. [PMID: 15219787 DOI: 10.1016/j.steroids.2004.03.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/22/2003] [Revised: 02/23/2004] [Accepted: 03/10/2004] [Indexed: 11/20/2022]
Abstract
Crystal structures of p-xylene-crystallized deoxycholic acid (3alpha,12alpha-dihydroxy-5beta-cholan-24-oic acid) and its three epimers (3beta,12alpha-; 3alpha,12beta-; and 3beta,12beta-) have been solved. Deoxycholic acid forms a crystalline (P21) complex with the solvent with a 2:1 stoichiometry whereas crystals of the three epimers do not form inclusion compounds. Crystals of the 3beta,12beta-epimer are hexagonal, whereas the 3alpha,12beta-and 3beta,12alpha-epimers crystallize in the P2(1)2(1)2(1) orthorhombic space group. The three hydrogen bond sites (two hydroxy groups, i. e. O3-H, and O12-H, and the carboxylic acid group of the side chain, O24bO24a-H) simultaneously act as hydrogen bond donors and acceptors. The hydrogen bond network in the crystals was analyzed and the following sequences have been observed: two chains (abcabc... or acbacb... ) and two rings (abc or acb), which constitute a complete set of all the possible sequences which can be drawn for an intermolecular hydrogen bond network formed by three hydrogen bond donor/acceptor sites forming crossing hydrogen bonds. The orientation of O3-H (alpha or beta) determines the sequence of the acceptor and the donor groups involved in the pattern: O24a --> O12 --> O3 --> O24b when it is alpha and O24a --> O3 --> O12--> O24B when it is beta. These observations were used to predict the hydrogen bond network of p-xylene-crystallized 3-oxo,12alpha-hydroxy-5beta-cholan-24-oic acid. This compound has two hydrogen bond donor and three potential hydrogen bond acceptor sites. According to the previous sequence set, this compound should crystallize in the monoclinic P21 system, should form a complex with the solvent, O24b should not participate in the hydrogen bond network, and the chain sequence O24a --> O12 --> O3 would be followed. All predictions were confirmed experimentally.
Collapse
Affiliation(s)
- A Jover
- Departamentos de Química Física y Física Aplicada, Facultade de Ciencias, Universidade de Santiago, Campus de Lugo, 27002 Lugo, Spain
| | | | | | | | | | | | | |
Collapse
|
6
|
Sood A, Panchagnula R. Peroral route: an opportunity for protein and peptide drug delivery. Chem Rev 2001; 101:3275-303. [PMID: 11840987 DOI: 10.1021/cr000700m] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- A Sood
- Department of Pharmaceutics, National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, S.A.S. Nagar, Punjab 160 062, India
| | | |
Collapse
|
7
|
Bolder U, Trang NV, Hagey LR, Schteingart CD, Ton-Nu HT, Cerrè C, Elferink RP, Hofmann AF. Sulindac is excreted into bile by a canalicular bile salt pump and undergoes a cholehepatic circulation in rats. Gastroenterology 1999; 117:962-71. [PMID: 10500080 DOI: 10.1016/s0016-5085(99)70356-2] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
BACKGROUND & AIMS Dihydroxy bile acids induce a bicarbonate-rich hypercholeresis when secreted into canalicular bile in unconjugated form; the mechanism is cholehepatic shunting. The aim of this study was to identify a xenobiotic that induces hypercholeresis by a similar mechanism. METHODS Five organic acids (sulindac, ibuprofen, ketoprofen, diclofenac, and norfloxacin) were infused into rats with biliary fistulas. Biliary recovery, bile flow, and biliary bicarbonate were analyzed. Sulindac transport was further characterized using Tr(-) rats (deficient in mrp2, a canalicular transporter for organic anions), the isolated perfused rat liver, and hepatocyte membrane fractions. RESULTS In biliary fistula rats, sulindac was recovered in bile in unconjugated form and induced hypercholeresis of canalicular origin. Other compounds underwent glucuronidation and were not hypercholeretic. In the isolated liver, sulindac had delayed biliary recovery and induced prolonged choleresis, consistent with a cholehepatic circulation. Sulindac was secreted normally in Tr(-) rats, indicating that its canalicular transport did not require mrp2. In the perfused liver, sulindac inhibited cholyltaurine uptake, and when coinfused with cholyltaurine, induced acute cholestasis. With both basolateral and canalicular membrane fractions, sulindac inhibited cholyltaurine transport competitively. CONCLUSIONS Sulindac is secreted into bile in unconjugated form by a canalicular bile acid transporter and is absorbed by cholangiocytes, inducing hypercholeresis. At high flux rates, sulindac competitively inhibits canalicular bile salt transport; such inhibition may contribute to the propensity of sulindac to induce cholestasis in patients.
Collapse
Affiliation(s)
- U Bolder
- Division of Gastroenterology, Department of Medicine, University of California, San Diego, California, USA
| | | | | | | | | | | | | | | |
Collapse
|
8
|
Hagey LR, Schteingart CD, Rossi SS, Ton-Nu HT, Hofmann AF. An N-acyl glycyltaurine conjugate of deoxycholic acid in the biliary bile acids of the rabbit. J Lipid Res 1998. [DOI: 10.1016/s0022-2275(20)32466-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
|
9
|
Kramer W, Wess G, Enhsen A, Falk E, Hoffmann A, Neckermann G, Schubert G, Urmann M. Modified bile acids as carriers for peptides and drugs. J Control Release 1997. [DOI: 10.1016/s0168-3659(96)01599-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
|
10
|
|
11
|
Roda A, Pellicciari R, Polimeni C, Cerrè C, Forti GC, Sadeghpour B, Sapigni E, Gioacchini AM, Natalini B. Metabolism, pharmacokinetics, and activity of a new 6-fluoro analogue of ursodeoxycholic acid in rats and hamsters. Gastroenterology 1995; 108:1204-14. [PMID: 7698590 DOI: 10.1016/0016-5085(95)90221-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
BACKGROUND/AIMS The effectiveness of ursodeoxycholic acid in treating biliary liver diseases is limited by low bioavailability and moderate activity. A new analogue of ursodeoxycholic acid was synthesized with a fluorine atom in position 6 because this should have resulted in an analogue more hydrophilic than ursodeoxycholic acid but with similar detergency. METHODS After synthesis, detergency, solubility, and lipophilicity of the 6-fluoro analogue in aqueous solution were determined and compared with those of natural analogues. Stability toward 7-dehydroxylation was assessed in human stools, pharmacokinetics and metabolism were evaluated in bile fistula rats and hamsters, accumulation in bile with long-term feeding was assessed in the hamsters, and the ability to prevent the hepatotoxic effects of taurochenodeoxycholic acid was evaluated in bile fistula rats after intraduodenal coinfusion. RESULTS 6-Fluoro-ursodeoxycholic acid was more stable than its parent molecule toward 7-dehydroxylation, it was efficiently secreted in bile, and its total recovery was very high. With long-term administration of 6-fluoro-ursodeoxycholic acid, taurine and glycine amidates accounted for more than 60% of the total biliary bile acids (15% ursodeoxycholic acid). The 6-fluoro analogue prevented the hepatotoxic effects of taurochenodeoxycholic acid. CONCLUSIONS The results suggest that 6-fluoro-ursodeoxycholic acid has considerable potential as a pharmaceutical agent in the treatment of cholestatic liver disease.
Collapse
Affiliation(s)
- A Roda
- Dipartimento di Scienze Farmaceutiche, Università di Bologna, Italy
| | | | | | | | | | | | | | | | | |
Collapse
|
12
|
Roda A, Pellicciari R, Cerrè C, Polimeni C, Sadeghpour B, Marinozzi M, Forti GC, Sapigni E. New 6-substituted bile acids: physico-chemical and biological properties of 6 alpha-methyl ursodeoxycholic acid and 6 alpha-methyl-7-epicholic acid. J Lipid Res 1994. [DOI: 10.1016/s0022-2275(20)39933-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
13
|
|
14
|
Kramer W, Girbig F, Gutjahr U, Kowalewski S, Jouvenal K, Müller G, Tripier D, Wess G. Intestinal bile acid absorption. Na(+)-dependent bile acid transport activity in rabbit small intestine correlates with the coexpression of an integral 93-kDa and a peripheral 14-kDa bile acid-binding membrane protein along the duodenum-ileum axis. J Biol Chem 1993. [DOI: 10.1016/s0021-9258(17)46808-6] [Citation(s) in RCA: 90] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
|
15
|
Aldini R, Roda A, Lenzi PL, Ussia G, Vaccari MC, Mazzella G, Festi D, Bazzoli F, Galletti G, Casanova S. Bile acid active and passive ileal transport in the rabbit: effect of luminal stirring. Eur J Clin Invest 1992; 22:744-50. [PMID: 1478243 DOI: 10.1111/j.1365-2362.1992.tb01439.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The intestinal absorption of bile acids (BA) with different chemical structure has been evaluated in the rabbit, after intestinal infusion of different concentrations (0.25-30 mM) of BA, by mesenteric blood sampling. Cholic (CA), chenodeoxycholic (CDCA), ursodeoxycholic (UDCA) acid, free and taurine (T-) conjugated, together with glycocholic (GCA) acid and deoxycholic acid (DCA) were studied. The apparent uptake parameters were calculated. All conjugated BA showed active transport (T max, nmol min-1 cm-1 int.), with Tmax values in the following order: TCA > TUDCA > TCDCA; unconjugated BA showed passive uptake, with values in the following order: DCA > CDCA > UDCA > CA. GCA and CA showed both passive uptake and active transport. For all BA studied the % uptake in the ileal segment considered was less than 10%, BA uptake being thus limited by transport and/or diffusion kinetics, rather than by flow velocity. The liquid resistance to BA radial diffusion inside the lumen was evaluated, and the infusate-to-blood uptake parameters corrected for it, in order to get the uptake parameters from the epithelium-to-liquid interface to mesenteric blood: the apparent Km decreased, passive uptake coefficient increased, while Tmax was unchanged. The passive component of the uptake, corrected for the luminal resistance, correlated with the BA hydrophobicity (r = 0.963; P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Collapse
Affiliation(s)
- R Aldini
- Istituto di Scienze Chimiche, Università di Bologna, Italy
| | | | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Gu JJ, Hofmann AF, Ton-Nu HT, Schteingart CD, Mysels KJ. Solubility of calcium salts of unconjugated and conjugated natural bile acids. J Lipid Res 1992. [DOI: 10.1016/s0022-2275(20)41428-2] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
|
17
|
|
18
|
Batta AK, Aggarwal SK, Salen G, Shefer S. Selective reduction of oxo bile acids: synthesis of 3 beta-, 7 beta-, and 12 beta-hydroxy bile acids. J Lipid Res 1991. [DOI: 10.1016/s0022-2275(20)41994-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
|
19
|
Marcus SN, Schteingart CD, Marquez ML, Hofmann AF, Xia Y, Steinbach JH, Ton-Nu HT, Lillienau J, Angellotti MA, Schmassmann A. Active absorption of conjugated bile acids in vivo. Kinetic parameters and molecular specificity of the ileal transport system in the rat. Gastroenterology 1991; 100:212-21. [PMID: 1983823 DOI: 10.1016/0016-5085(91)90603-i] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Active transport of conjugated bile acids by the distal ileum is required for efficient enterohepatic cycling of bile acids. Experiments were performed in the rat to obtain accurate values for Tmax and Michaelis constant (Km) of the absorptive area of the rat ileum and to define the structural specificity of the transport system. The distal fifth (20 cm) of the small intestine from an anesthetized animal with a biliary fistula was perfused using solutions of 10 taurine-conjugated bile acids; a flow rate was used that was sufficiently high such that unstirred water layer effects were negligible and the intraluminal concentration remained unchanged throughout the perfused segment. The absorption rate was equated with the rate of hepatic bile acid secretion. Values of Tmax (mumol/min.kg) were markedly influenced by bile acid structure: cholyltaurine, 12.9; ursocholyltaurine, 9.6; ursodeoxycholyl taurine, 5.0; and lagodeoxycholyl-(3 alpha,12 beta-dihydroxy-cholanoic acid)-taurine, 1.2. Decreasing the length of the side chain of ursodeoxycholate conjugates from 8 to 6 carbon atoms was associated with a modest increase in Tmax values from 5.0 to 9.1 mumols/min.kg. Values of Km correlated with Tmax values and ranged from 0.5 to 5 mmol/L, being highest for those bile acids that were best transported. The Tmax for cholyltaurine transport was not reached when the intraluminal concentration was as high as its critical micellization concentration, precluding the definition of its Tmax; however, for ursocholyltaurine, with a critical micellization concentration of 40 mmol/L, saturation of transport was clearly shown. Kinetic parameters could not be obtained for two common dihydroxy conjugates (chenodeoxycholyltaurine and deoxycholyltaurine) because at a transport rate of 2 mumols/min.kg systemic toxicity and death occurred. These studies define the maximal transport capacity of the rat ileum for taurine-conjugated bile acids; they indicate that the ileal transport system in the rat is of low affinity and high capacity for taurine conjugates of hydrophilic bile acids, and they show that both nuclear substituents and side chain length influence the transport rate of taurine-conjugated bile acids.
Collapse
Affiliation(s)
- S N Marcus
- Department of Medicine, University of California, San Diego, La Jolla
| | | | | | | | | | | | | | | | | | | |
Collapse
|