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A F Hofmann

Publications and source records attributed to A F Hofmann.

At least 73 records · Page 4Linked to original sources
PubMed1995

Method for removal of surface-active impurities and calcium from conjugated bile salt preparations: comparison with silicic acid chromatography.

Some commercial preparations of common natural conjugated bile salts contain impurities (e.g., amines, lipids, and calcium) that are likely to affect their physicochemical properties. A method was developed for purifying commercial preparations of sodium salts of glycine- and taurine-conjugated bile acids. The method consists of passage of a dilute aqueous solution of the sodium bile salt through three columns in sequence: graphitized carbon, a hydrophobic bonded octadecylsilane (C18) cartridge, and a calcium-chelating resin. The final solution was extracted with chloroform, and the purified bile salt was then isolated by freeze-drying, with a yield of 65-75%. Each bile salt purified by this method was compared with the corresponding bile salt purified by conventional adsorption chromatography on a silicic acid column, using a mixture of methanol and chloroform as eluant. Purity was assessed by visible spectra, by surface tension measurements (using the maximum bubble-pressure method and a Wilhelmy wire method), by chloroform extractability of impurities in the conjugated bile acid, by liposome solubilization, and by chemical analysis of the calcium content. Both purification methods removed colored and surface-active impurities, but the new method was always as or more effective than silicic acid column chromatography. Calcium ion, present in commercial bile salts in concentrations up to 16 mmol/mol bile salt, was removed completely by the three-column method, but not by silicic acid chromatography. The new method is thus a simple, rapid, and efficient procedure for purification of the sodium salts of glycine- and taurine-conjugated bile acids for physicochemical measurements, in which elimination of surface-active impurities and polyvalent cations is desired.

Bile Acids and Salts↗
PubMed1994

Expression and characterization of a functional rat liver Na+ bile acid cotransport system in COS-7 cells.

A cDNA for the rat liver sodium-dependent bile acid cotransporter was expressed in COS-7 cells to study the functional properties of the translated protein in a mammalian cell line. A 1.2-kb insert was ligated into a pMAMneo vector and transiently transfected using electroporation. After optimal conditions were established, the transiently transfected COS cells were screened with fluorescent-conjugated labeled bile acids for evidence of expression of the cotransporter after 48 h. The uptake of [3H]taurocholate ([3H]TC) was then determined in cells transfected with or without the bile acid insert. Progressive uptake of [3H]TC (0.45 microM) was observed for 30 min in the presence of sodium. In contrast, no uptake of [3H]TC was observed in the absence of sodium, in nontransfected COS cells, or in COS cells transfected with the empty plasmid. Kinetic studies revealed a Michaelis constant (Km) of 29 microM, essentially identical to the Km of this cotransporter described in intact rat hepatocytes and membrane vesicles. Uptake of [3H]TC (5.0 microM) at 5 min (n = 3-6) was inhibited by 100 microM taurochenodeoxycholic acid (81%), tauroursodeoxycholic acid (77%), cholic acid (55%), chenodeoxycholic acid (74%), and ursodeoxycholic acid (56%) but not by 100 microM taurodehydrocholate, 1 mM probenecid, or 100 microM bilirubin. In contrast, bumetanide (500 microM) inhibited [3H]TC uptake by 52%. These studies indicate that the isolated cDNA codes for a physiological bile acid transporter present in rat hepatocytes and that posttranslational factors present in mammalian cells may not be as important in defining properties of this cotransport system.

Animals↗
PubMed1994

Pharmacology of ursodeoxycholic acid, an enterohepatic drug.

The pharmacokinetics, metabolism, as well as the pharmacodynamic actions of ursodeoxycholic acid are reviewed and related to its physicochemical properties. Ursodeoxycholic acid is absorbed incompletely because of its low aqueous solubility. After absorption, it is conjugated with glycine or taurine and circulates with the endogenous bile acids. At usual doses (8-10 mg/kg/day), the pool of ursodeoxycholyl conjugates constitutes 30-60% of circulating bile acids. Ursodeoxycholic acid is metabolized by intestinal bacteriae to lithocholic acid which does not accumulate in the circulating bile acids because of efficient hepatic sulfation. Administration of ursodeoxycholic acid causes decreased cholesterol absorption, increased bile acid biosynthesis, and decreased biliary cholesterol secretion. Ursodeoxycholic acid is a choleretic agent, as all bile acids, but differs from other dihydroxy-bile acids in being non-cytotoxic because it has less affinity for membranes, and when present at micellar concentrations does not solubilize membranes. Chronic administration of ursodeoxycholic acid appears to increase canalicular transport.

Bile Acids and Salts↗
PubMed1994

Bile acid metabolism and biliary secretion in patients receiving orthotopic liver transplants: differing effects of cyclosporine and FK 506.

Bile acid metabolism and biliary secretion were characterized in the first 2 wk after orthotopic liver transplantation in 15 patients receiving cyclosporine and in five patients receiving FK 506. Analyses were performed on hepatic bile obtained by T-tube drainage; values obtained were compared with literature values for bile samples obtained in patients who had undergone cholecystectomy. Biliary bile acid output, which is equivalent to bile acid biosynthesis from cholesterol, was low (mean +/- S.E.M.) and increased with time: day 1, 0.50 +/- 0.1 mmol/day; day 3, 0.8 +/- 0.1 mmol/day; and day 6, 1.6 +/- 0.5 mmol/day. Chenodeoxycholic acid biosynthesis, as percent of total bile acid biosynthesis, was abnormally low in patients receiving cyclosporine (16.2 +/- 1.1) but not in patients receiving FK 506 (38.2 +/- 4.8) (p < 0.005). Before the T-tube was clamped, the proportion of deoxycholic acid (a secondary bile acid formed by bacterial 7-dehydroxylation of cholic acid) was low in both groups: cyclosporine, 0.4 +/- 0.1; FK 506, 4.8 +/- 2.5 (p < 0.01). The mean concentration of bile acids in hepatic bile between days 4 and 11 did not differ significantly between groups: cyclosporine, 7.7 +/- 1.3 mmol/L; FK 506 4.3 +/- 0.7 mmol/L (mean +/- S.E.M.). (These values are similar to those reported for patients who have undergone cholecystectomy.) Bile acid-dependent bile flow, expressed as apparent choleretic activity (microliters of bile per micromole of bile acid output), was markedly elevated: in patients receiving cyclosporine the value was 129, and in patients receiving FK 506 the value was 220. (In patients who have undergone cholecystectomy, this value is less than 30).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Biliary bile acids of fruit pigeons and doves (Columbiformes): presence of 1-beta-hydroxychenodeoxycholic acid and conjugation with glycine as well as taurine.

The biliary bile acid composition of 30 species of pigeons and doves belonging to seven genera in the avian order Columbiformes was determined using TLC, HPLC, GLC/MS, LSIMS, and NMR. In 23 of 25 species of fruit pigeons and doves, chenodeoxycholic acid was the major bile acid (> 50%). In only 1 species (Ptilinopus ornatus) was cholic the major bile acid. A number of species (7 of 15 species in the genus Ptilinopus, and 6 of 9 species in the genus Ducula) contained 1 beta,3 alpha,7 alpha-trihydroxy-5 beta-cholan-24-oic acid in proportions ranging from 2 to 43%. This 1 beta-hydroxy derivative of chenodeoxycholic acid has not been previously identified as a major biliary bile acid in vertebrates. Five of 15 species of the genus Ptilinopus, 5 of 9 species of the genus Ducula, and the only species examined for the genus Gymnophaps contained 23R-hydroxy chenodeoxycholic acid in detectable proportions, ranging from 1 to 4%. Bile acids were conjugated (in N-acyl linkage) with glycine and taurine in 28 species and with only taurine in 2 species. The fruit pigeons are the first non-mammalian genera identified to date in whom bile acids are conjugated with glycine, as well as with taurine. An incidental finding was that a gallbladder was present in 3 genera (Ptilinopus, Ducula, and Gymnophaps) and absent in 4 genera (Gallicolumba, Chalcophaps, Otidiphaps, and Treron).

Animals↗
PubMed1994

Effects of side chain length on ionization behavior and transbilayer transport of unconjugated dihydroxy bile acids: a comparison of nor-chenodeoxycholic acid and chenodeoxycholic acid.

13C-NMR spectroscopy was used to examine the effect of side chain length on the ionization properties and transmembrane transport rate of 3 alpha,7 alpha-dihydroxy bile acids. When solubilized in taurocholate micelles, [23-13C]nor-chenodeoxycholic acid (nor-CDCA) had a pKa of 6.1, similar to that of CDCA (pKa 6.2), its C24 homologue. In unilamellar phosphatidylcholine vesicles, the pKa of nor-CDCA was 7.0, whereas that of CDCA was 6.6. Lineshape analysis indicated that the rate of ionization of nor-CDCA as a micellar solute or as a vesicle component was very slow (0.4 x 10(5) sec-1) compared to that of acetic acid in water (8.7 x 10(5) sec-1). Lineshape analysis of spectra of the protonated form of nor-CDCA at acidic bulk pH indicated that the transbilayer transport rate of nor-CDCA (580 sec-1) was six times faster than that of CDCA (100 sec-1). It is proposed that the shorter side chain of the nor-CDCA molecule causes it to reside more deeply inside the vesicle bilayer than CDCA, explaining its weaker ionization and more rapid flip-flop rate. These in vitro experiments imply that, in vivo, a given C23 nor-dihydroxy bile acid will ionize less readily when present in membranes, and it will also flip-flop faster than its C24 homologue.

Biological Transport↗
PubMed1993

Transcriptional regulation of cholesterol 7 alpha-hydroxylase mRNA by conjugated bile acids in primary cultures of rat hepatocytes.

The role of bile acids in the regulation of cholesterol 7 alpha-monooxygenase (EC 1.14.13.17) was characterized using primary cultures of rat hepatocytes supplemented with dexamethasone and thyroxine. Taurocholate and taurodeoxycholate (50 microM) repressed cholesterol 7 alpha-hydroxylase mRNA to 44 +/- 9 and 52 +/- 4%, respectively, of control values. Repression by these natural, relatively hydrophobic bile acids was concentration dependent, with an IC50 of about 50 microM, and time dependent with a t1/2 for repression of 22 h. In contrast, two natural hydrophilic bile acids, tauroursodeoxycholate and taurohyodeoxycholate, had no effect on cholesterol 7 alpha-hydroxylase mRNA levels. Taurochenodeoxycholate and taurolithocholate also had no effect, but these hydrophobic bile acids were rapidly hydroxylated to more hydrophilic bile acids. Hydrophilic bile acid analogues (nor (C23) bile acids and beta-hydroxy epimers) repressed cholesterol 7 alpha-hydroxylase mRNA less potently than their corresponding and more hydrophobic C24 or alpha-hydroxy derivatives. Cholesterol 7 alpha-hydroxylase specific activity was decreased by taurocholate or taurodeoxycholate (50 microM) to 26 +/- 9 and 56 +/- 3% of control, respectively; its transcriptional activity was repressed to 52 +/- 5% of control by taurocholate (50 microM). The addition of cholesterol or the induction of cholesterol biosynthesis did not influence repression of cholesterol 7 alpha-hydroxylase mRNA levels by taurocholate. Based on several lines of evidence, cAMP was not involved in bile acid-induced repression. In rat hepatocytes cultured under conditions in which cholesterol 7 alpha-hydroxylase gene expression is maintained at in vivo levels, hydrophobic bile acids repress this enzyme at the level of gene transcription independently of cholesterol availability.

Animals↗
PubMed1993

5 beta-hydroxylation by the liver. Identification of 3,5,7-trihydroxy nor-bile acids as new major biotransformation products of 3,7-dihydroxy nor-bile acids in rodents.

24-Norursodeoxycholic acid (nor-UDCA), when administered into the anesthetized biliary fistula hamster or injected into the perfusate of an isolated liver, was hydroxylated at C-5 to give 5 beta-hydroxynorursodeoxycholic acid 2 (3 alpha,5,7 beta-trihydroxy-24-nor-5 beta-cholan-23-oic acid), which was secreted into bile mainly as such. Similarly, 24-norchenodeoxycholic acid (nor-CDCA) was 5 beta-hydroxylated to give 5 beta-hydroxynor-chenodeoxycholic acid 4 (3 alpha,5,7 alpha-trihydroxy-24-nor-5 beta-cholan-23-oic acid), which was also secreted into bile without appreciable further biotransformation. The site of hydroxylation was assigned by 13C and 1H NMR and mass spectrometry. 5-Hydroxylation was a major biotransformation pathway at physiological bile acid loads. 5-Hydroxylation of UDCA also occurred in the perfused rat liver but to a lesser extent. 5-Hydroxylation of nor-UDCA was not observed in rabbit, dog, or man, indicating that its formation is species-specific. 5-Hydroxylation of nor-CDCA and nor-UDCA is the first reported example of hydroxylation of a tertiary carbon atom of bile acids. Nor-dihydroxy bile acids appear to be useful for the detection of minor hydroxylation pathways, because their prolonged hepatobiliary retention exposes them repeatedly to hydroxylases present in the hepatobiliary system.

Animals↗
PubMed1993

Solitary versus multiple cholesterol gallbladder stones. Mechanisms of formation and growth.

The development and growth pattern of solitary and multiple cholesterol gallbladder stones was defined using cholecystography in a prospective study of 48 patients whose initial cholecystograms indicated a stone-free gallbladder and who developed gallstones within the subsequent 5 years. Radiological observations performed over 365 patient-years were complemented by macroscopic examination, radiograms, scanning electron microscopy, and chemical analysis of gallstones from these and other patients obtained at cholecystectomy. Solitary gallstones were found to develop after a precursor phase of over 2 years during which free-floating crystal laminae of cholesterol formed. These laminae subsequently aggregated loosely and underwent external compaction and internal remodeling by movement of cholesterol molecules to form compact spheroids. A single lamina was observed to function as a nucleus for the development of a solitary stone shaped as an ellipsoid. About 10% of solitary stones were found to have a solitary pigment stone in their center. In contrast, multiple cholesterol gallstones formed without a precursor phase. Innumerable, very thin cholesterol crystals appeared which very abruptly aggregated to form spheres of up to 1 mm in diameter. Within 3 months a second aggregation took place in which these spheres colaesced to form mulberry stones. Mulberry stones in turn were transformed either to faceted stones (if many were present in the gallbladder) or to barrel stones (if few were present) over a period of 3 years. It is proposed that temporary occlusion of the cystic duct leads to supersaturation of bile with calcium bilirubinate and/or calcium carbonate which in turn promotes deposition of either or both of these calcium salts on the surface of single or multiple gallstones. For multiple gallstones, this process or the deposition of additional cholesterol crystals seals the gallstone surface and is followed by metamorphosis of the stone center.

Adult↗
PubMed1993

Cholylsarcosine, a new bile acid analogue: metabolism and effect on biliary secretion in humans.

BACKGROUND: Cholylsarcosine, the synthetic conjugate of cholic acid and sarcosine, is resistant to deconjugation-dehydroxylation during enterohepatic cycling in rodents and improves lipid absorption in a canine model of intestinal bile acid deficiency caused by distal intestinal resection. Experiments were performed to define its metabolism and effect on biliary secretion in humans. METHODS: The circulating bile acid pool was labeled with [14C]cholylsarcosine, and its turnover rate and biotransformation were determined by sampling bile daily. Cholylsarcosine (or cholyltaurine) was infused into the duodenum for 8 hours to define its effect on bile flow and biliary lipid secretion. RESULTS: Cholylsarcosine was lost rapidly from the enterohepatic circulation with a t1/2 of 0.5 days. The compound was not biotransformed by hepatic or bacterial enzymes. Cholylsarcosine had choleretic activity similar to that of cholyltaurine but induced more phospholipid and cholesterol secretion than cholyltaurine in four or five subjects. Infusion of cholylsarcosine (or cholyltaurine) at a rate averaging 0.6 mumol.min-1.kg-1 gave a biliary recovery of 0.2 mumol.min-1.kg-1; this value is the Tmax for active ileal transport of conjugated bile acids in humans. Laboratory tests for liver injury remained within normal limits. CONCLUSIONS: In humans, cholylsarcosine is not metabolized, is nontoxic, and has similar effects on biliary secretion as cholyltaurine. It appears safe to test in long-term studies the effect of cholylsarcosine on bile acid-deficiency states in humans.

Adult↗
PubMed1993

Negative feedback regulation of the ileal bile acid transport system in rodents.

BACKGROUND: Active transport of conjugated bile acids by ileal enterocytes is a key mechanism for conservation of the bile acid pool. Experiments were performed to determine whether such transport is regulated by substrate load. METHODS: Using anesthetized biliary fistula guinea pigs or rats, the ileum was perfused with ursodeoxycholyltaurine at a concentration causing maximal ileal transport of this bile acid; absorption was assessed by biliary recovery. Before ileal perfusion, animals ingested one of three diets: chow, chow with added conjugated bile acid, or chow with added cholestyramine. RESULTS: In the guinea pig, ingestion of a taurocholate-enriched diet resulted in a 75% decrease in the absorption rate of ursodeoxycholyltaurine. Similar results were obtained with cholylsarcosine (a deconjugation-dehydroxylation resistant analogue) or with chenodeoxycholylglycine, the endogenous bile acid of the guinea pig. In contrast, cholestyramine ingestion caused an increase in ursodeoxycholyltaurine absorption. In the rat, cholyltaurine or cholylsarcosine ingestion also caused decreased ileal transport. In the guinea pig, maximal down-regulation of active ileal bile acid transport occurred after 2-3 days of bile acid feeding; up-regulation required 3-4 days. CONCLUSIONS: Bile acid metabolism is regulated by feedback inhibition of active ileal transport in addition to the well-established feedback inhibition of bile acid biosynthesis in the liver. Together, these two regulatory mechanisms ensure constancy of bile acid secretion.

Animals↗
PubMed1993

Primary and secondary prevention of gallstone disease: implications for patient management and research priorities.

Primary prevention is defined as the prevention of gallstone formation; secondary prevention is defined as the prevention of clinical manifestations of gallstones--symptoms or more severe complications. For primary prevention, general "wellness" measures can be recommended from a theoretic standpoint. These include elimination of obesity (to decrease excessive cholesterol biosynthesis or mobilization of tissue cholesterol during rapid weight loss); a high-fiber, high-calcium diet (to diminish input of deoxycholic acid); ingestion of meals at regular intervals (to diminish gallbladder storage and interruption of the enterohepatic circulation of bile acids); and vigorous exercise (to permit frequent meals without excessive caloric intake). In addition, based on animal studies, intake of low saturated fatty acids may diminish the nucleation of supersaturated bile. Secondary prevention is recommended only when gallstones become symptomatic because of the benign natural history of asymptomatic gallstones, the intrinsic limitations of medical therapy, and the absence of predictors that would enable selection of asymptomatic patients at high risk for becoming symptomatic. Secondary prevention involves nonsurgical approaches (dissolution with ursodiol, extracorporeal shock-wave lithotripsy plus adjuvant bile acids, and, rarely, contact dissolution with organic solvents). For patients with symptomatic gallstones, nonsurgical therapy will be used by those patients who cannot or will not have surgery, as well as those patients who wish to explore a trial of nonsurgical therapy before having surgery. Because of the intrinsic limitations of nonsurgical therapy in comparison to the efficacy and safety of surgery, most patients will undergo surgery. Future research priorities include elucidation of factors responsible for: (1) bile that is supersaturated in cholesterol; (2) elevated biliary deoxycholic acid levels in patients with cholesterol gallstones; (3) rapid nucleation in patients with multiple cholesterol gallstones; (4) precipitation of calcium bilirubinate; and (5) impaired gallbladder motility in gallbladder stone disease.

Animals↗
PubMed1993

Ursodeoxycholic acid in the Ursidae: biliary bile acids of bears, pandas, and related carnivores.

The biliary bile acid composition of gallbladder bile obtained from six species of bears (Ursidae), the Giant panda, the Red panda, and 11 related carnivores were determined by reversed phase liquid chromatography and gas chromatography-mass spectrometry. Bile acids were conjugated solely with taurine (in N-acyl linkage) in all species. Ursodeoxycholic acid (3 alpha, 7 beta-dihydroxy-5 beta-cholan-24-oic acid) was present in all Ursidae, averaging 1-39% of biliary bile acids depending on the species; it was not detected or present as a trace constituent (< 0.5%) in all other species, including the Giant panda. Ursodeoxycholic acid was present in 73 of 75 American Black bears, and its proportion averaged 34% (range 0-62%). Ursodeoxycholic acid averaged 17% of biliary bile acids in the Polar bear (n = 4) and 18% in the Brown bear (n = 6). Lower proportions (1-8%) were present in the Sun bear (n = 2), Ceylon Sloth bear (n = 1), and the Spectacled bear (n = 1). Bile of all species contained taurine-conjugated chenodeoxycholic acid and cholic acid. In some related carnivores, deoxycholic acid, the 7-dehydroxylation product of cholic acid, was also present. To determine whether the 7 beta hydroxy group of ursodeoxycholic acid was formed by hepatic or bacterial enzymes, bile acids were determined in hepatic bile obtained from bears with chronic biliary fistulae. Fistula bile samples contained ursodeoxycholic acid, chenodeoxycholic acid, and a trace amount of cholic acid, all as taurine conjugates, indicating that ursodeoxycholic acid is a primary bile acid formed in the liver in Ursidae.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Increased blood levels of methyl tert-butyl ether but not of ethyl propionate during instillation with contact gallstone dissolution agents in the pig.

We performed experiments in anesthetized piglets with two cholesterol gallstone solvents, methyl tert-butyl ether and ethyl propionate, to determine whether blood levels of either solvent would increase during gallbladder instillation of these solvents under conditions simulating gallstone dissolution. The solvent was oscillated rapidly in and out of the gallbladder with a computer-controlled syringe pump; intraluminal pressure was set below the leakage pressure, and oscillating volume was set below the leakage volume to decrease loss of solvent into the intestine. Blood levels were measured with gas chromatography. Six piglets received methyl tert-butyl ether, and six piglets received ethyl propionate. During 2 hr of instillation with methyl tert-butyl ether, blood levels increased steadily to concentrations averaging 0.3 ml/L blood at 2 hr; during a 6-hr period of instillation, blood levels rose to above 0.4 ml/L blood. Replacement of methyl tert-butyl ether with saline solution in the gallbladder caused blood levels to decline gradually; plasma levels decreased by half in 90 min. In contrast, when ethyl propionate was infused for 2 or 6 hr, blood levels remained below the detection limit, probably because of high first-pass hepatic extraction. We conclude that, under conditions simulating those likely present in patients undergoing contact dissolution of gallbladder stones, the two solvents differ: Ethyl propionate is removed so rapidly from blood that its levels remain undetectable, whereas methyl tert-butyl ether levels in blood (and, presumably, peripheral tissues) increase continuously.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗