A bioluminescence assay for total 3 alpha-hydroxy bile acids in serum using immobilized enzymes

Bile acids: trying to understand their chemistry and biology with the hope of helping patients

An informal review of the author's five decades of research on the chemistry and biology of bile acids in health and disease is presented. The review begins with a discussion of bile acid structure and its remarkable diversity in vertebrates. Methods for tagging bile acids with tritium for metabolic or transport studies are summarized. Bile acids solubilize polar lipids in mixed micelles; progress in elucidating the structure of the mixed micelle is discussed. Extensive studies on bile acid metabolism in humans have permitted the development of physiological pharmacokinetic models that can be used to simulate bile acid metabolism. Consequences of defective bile acid biosynthesis and transport have been clarified, and therapy has been developed. Methods for measuring bile acids have been improved. The rise and fall of medical and contact dissolution of cholesterol gallstones is chronicled. Finally, principles of therapy with bile acid agonists and antagonists are given. Advances in understanding bile acid biology and chemistry have helped to improve the lives of patients with hepatobiliary or digestive disease.

Determination of total bile acid levels using a thick-film screen-printed Ir/C sensor for the detection of liver disease

An electrochemical sensor, based on thick-film screen-printed Ir/C working and counter electrodes, was developed for the detection of total bile acid concentration in a physiological fluid for potential patient management in patients with liver disease. Current electrochemical methods of detecting total bile acid levels involve the use of potentials greater than +0.45 V, versus an Ag/AgCl reference electrode, and require a selectively permeable membrane. The proposed detection method did not require any membrane and used a potential of +0.27 V versus Ag/AgCl. This biosensor used 3-alpha-hydroxysteroid dehydrogenase (3alpha-HSD) (EC 1.1.1.50) immobilized on the thick-film screen-printed working electrode to detect the enzymatically generated NADH. The production of the NADH resulted from the reaction of the enzyme with bile acids such as sodium cholate, taurocholic and taurochenodeoxycholic acid, which could then be used to quantify the total bile acid. Constant potential measurements showed that this biosensor had good linear performance over a 0-200 microM concentration range in the phosphate buffer and the bovine serum. The sensor performance was also examined at different temperatures and pH conditions. This sensor prototype could be used for single use, disposable detection of total bile acids, extending its applicability for simple and early detection of liver disease.

Isolation and determination of bile acids

In this article, the methods of isolation and determination of bile acids are reviewed. Methods for separation of bile acids from cattle and pig bile are given in detail. Isolation of a mixture of cholic acid and deoxycholic acids from cattle bile and their subsequent purification are described. The isolation and purification of hyodeoxycholic acid and other components of pig bile are also included. Methods for the determination of bile acids in various biological samples are reviewed, including enzyme assays, radioimmunoassay, enzyme immunoassay and chromatographic methods. Among chromatographic methods, separation and determination of bile acids by thin-layer chromatography, gas chromatography and high performance liquid chromatography are reviewed. Particular attention is given to the use of high performance liquid chromatography since this has recently been the most commonly applied method for the separation and determination of bile acids.

Repeated administration of a vitamin preparation containing glycocholic acid in patients with hepatobiliary disease

BACKGROUND

Until now, hydrophilic and lipophilic vitamin preparations had to be administered separately during total parenteral nutrition. By addition of glycocholic acid, a vitamin supplement (Cernevit, Baxter, Heidelberg, Germany) was developed that combines all vitamins into one vial. However, little information exists about possible consequences of bile acid administration such as glycocholic acid, especially if liver disease is pre-existing.

AIM

To evaluate the effects of total parenteral nutrition with a vitamin preparation containing high doses of glycocholic acid in patients with and without liver disease.

METHODS

In a prospective, randomized-controlled trial, 74 patients, 36 of them with hepatobiliary disease, received total parenteral nutrition for 16 +/- 11 days, either with Cernevit or control vitamin supplements. Patients were closely monitored for clinical and biochemical parameters including serum bile acid profiles measured by high-performance liquid chromatography.

RESULTS

Serum glycocholic acid increased in patients with liver disease treated with Cernevit, whereas total bile acids did not significantly change. Other liver function tests remained stable during treatment. No adverse events during Cernevit administration were noted except for a reversible slight increase of transaminases in one patient.

CONCLUSIONS

Cernevit was well tolerated after repeated dosing, even in patients with severe liver disease. Apart from standard controls of liver biochemistry, no specific surveillance is necessary during treatment with Cernevit.

Measurement of bile acid in serum and bile with arylamine-glass-bound 3α-hydroxysteroid dehydrogenase and diaphorase

3Alpha-hydroxysteroid dehydrogenase (3-HSD) from Pseudomonas testosteroni and diaphorase (lipoyl dehydrogenase) from Clostridium spp. have been immobilized individually onto arylamine glass beads through diazotization. A cost-effective enzymic colorimetric method for determination of bile acid in serum and bile employing a mixture of these immobilized enzymes was developed. The method is based on measurement of reduced nicotinamide adenine dinucleotide generated from bile acid in serum/bile by immobilized 3alpha-HSD with a color reagent consisting of nitro blue tetrazolium chloride salt, oxidized nicotinamide adenine dinucleotide, and immobilized lipoyl dehydrogenase in 0.065 M sodium phosphate buffer, pH 7.0. Analytical recovery of added bile acid (50 and 200 micromol/L) was 95.57 and 85.46% in serum and 97.6 and 91.6% in bile, respectively. Within- and between-batch coefficients of variation (CV) for bile acid determination were <1.2 and <0.2% in serum and >0.1 and <0.1% in bile, respectively. Good correlations for bile acid in serum (r1=0.92) and in bile (r2=0.97) were obtained by use of a standard chemical method and the present method. The mixture of immobilized 3alpha-HSD dehydrogenase and lipoyl dehydrogenase lost 50% of its initial activity after 6 months of regular use. The cost of bile acid determination in 100 serum and bile samples by the present method has been compared with that of the Sigma kit method.

The effect of colestipol dose on postprandial serum bile acid concentration: assessment by an enzymic bioluminescence procedure

A dose-response study was performed with three doses of colestipol, using postprandial serum bile acid levels to assess bile acid sequestering activity in 40 volunteers with asymptomatic hyperlipidaemia. Subjects who entered the study had total serum cholesterol concentrations greater than 220 mg/dl and triglyceride concentrations less than 200 mg/dl. They were randomly assigned to one of four parallel treatment groups: (a) placebo b.d., (b) colestipol (as Colestid hydrochloride granules) 2.5 g b.d., (c) colestipol 5 g b.d., and (d) colestipol 7.5 g b.d. Subjects were maintained on a constant repeating solid diet throughout the 6-day study period, and colestipol was ingested 30 min before breakfast and dinner. No drug was administered on Days 1-3; baseline (pre-treatment) serum bile acid concentration profiles were determined on Day 3. The above treatments were given on Days 4-6, and total serum bile acid concentrations were determined at 30- or 60-min intervals for 10 h on Days 4 and 6. Serum bile acids were measured using a bioluminescence procedure which enzymically measures total 3 alpha hydroxy bile acids. Serum bile acid concentrations were significantly decreased from the pretreatment period by 5.0 and 7.5 g/day as compared to 2.5 g/day or placebo. Differences from the pre-treatment period in the area under the serum bile acid time curve revealed the same trends in the data as analysis of percentage difference (Day 6 vs pre-treatment period) in serum bile acid concentrations. These results indicate that postprandial serum bile acid concentrations are influenced by colestipol in a dose-related manner, with doses of 5 and 7.5 g b.d. having a significantly greater effect than 2.5 g b.d. The dose of 7.5 g b.d. had an identical effect on serum bile acid patterns as a dose of 5.0 g t.d.s., which was previously reported. Our findings also show that changes in serum bile acid concentrations may be used to follow the immediate effects of bile acid sequestration in hypercholes terolaemic subjects, and that the bioluminescence enzyme technique is sufficiently sensitive to detect such changes.

Taurohyocholate, taurocholate, and tauroursodeoxycholate but not tauroursocholate and taurodehydrocholate counteract effects of taurolithocholate in rat liver

The infusion of taurolithocholate (TLC) in vivo or in the isolated perfused liver of the rat causes cholestasis and cellular necrosis. In order to analyze the protective effect of bile salts differing in number and steric position of their hydroxy groups against TLC-induced cholestasis, isolated rat livers were perfused with taurocholate (TC), taurohyocholate (THC), tauroursocholate (TUC), taurodehydrocholate (TDHC), and tauroursodeoxycholate (TUDC) (16 and 32 mumol/l) with or without TLC (8 and 16 mumol/l). Bile flow, bile salt secretion, and the hydroxylation pattern of the bile salts secreted were analyzed. TLC caused complete cholestasis after 15 min of perfusion. All bile salts studied had a protective effect. THC, TC, and TUDC completely abolished the cholestasis induced by TLC while TUC did so only for the first 10 min. TDHC was protective only as long as it was biotransformed into hydroxyoxo bile salts. Coinfusion of bile salts did not influence uptake of TLC (greater than or equal to 93% of dose). Differences were found regarding the amount of TLC biotransformed (% of uptake): TC 50%; THC 32%; TUDC 36%; TUC 20%. Light microscopy revealed cellular necrosis, and dilated canaliculi were found in livers perfused with TLC only or in combination with TUC or TDHC, while the other bile salts prevented these changes. We conclude that bile salts with low micelle-forming capacity have little protective effect against TLC-induced cholestasis. These bile salts induce less biotransformation of TLC than TC, THC, and TUDC. The protective effect is not dependent on the hydrocholeretic effect of the added bile salt and is not due to an uptake inhibition.

Tauroursodeoxycholate prevents taurolithocholate-induced cholestasis and toxicity in rat liver

Ursodeoxycholate has been advocated for the treatment of cholestatic liver diseases. The coinfusion of tauroursodeoxycholate with taurolithocholate in the perfused rat liver completely prevented the decrease of bile flow and the increase of oxygen uptake found with taurolithocholate only. Bile flow and bile salt secretion were increased with the coinfusion of both bile acids as compared with the infusion of tauroursodeoxycholate only (+4.30 microliters/g liver per 30 min) with 16 and 32 mumol/l tauroursodeoxycholate (+1.55 microliters/g liver per 30 min with 80 and 160 mumol/l). Morphological examination revealed a 50% decrease of the number of necrotic cells in the periportal area. Tauroursodeoxycholate did not inhibit the uptake of taurolithocholate, but increased its transcellular passage and biotransformation. Thus, tauroursodeoxycholate prevents taurolithocholate-induced cholestasis and liver cell toxicity probably by an intracellular mechanism.

Bioluminescent assay for serum adenosine deaminase with immobilized bacterial luciferase

We describe a bioluminescence method for measuring adenosine deaminase activity in serum. The method involves use of batchwise enzyme reaction containing adenosine, alpha-ketoglutarate, glutamic dehydrogenase and NADH. The resulting solution is injected to the continuous-flow bioluminescence system. In the system, a bacterial luciferase and NAD(P)H:FMN oxidoreductase are covalently co-immobilized on Sepharose 4B. Carrier solution (pH 6.8) for bioluminescence reaction contains FMN and decanal. The continuous-flow light-emitting system, in which the reactor (flow cell packed with immobilized enzyme) is placed in front of a photomultiplier tube inside a photon counter, is versatile and simple. Concentration and response are linearly related from 1.2 to 92.5 pmol per injection of ammonia. The precision of the method is satisfactory (coefficient of variation 3.9-6.8%). We validated the technique by comparing results with conventional assay method (UV method). Normal values for adenosine deaminase activity of serum ranged from 7.0 to 22.0 U/l in agreement with those obtained by other method. The Sepharose 4B-immobilized enzymes are stable for more than one year. This assay system could be used as a routine clinical laboratory test in the diagnosis of liver damage.

Effect of the bile-acid sequestrant colestipol on postprandial serum bile-acid concentration: evaluation by bioluminescent enzymic analysis

Chronic ingestion of bile-acid sequestrants has been shown to decrease the serum cholesterol concentration and coronary events in hypercholesterolaemic patients. To develop improved sequestrants, a rapid, convenient method for testing the bile-acid binding efficacy of sequestrants is needed. Serum bile-acid concentrations could be used to detect bile-acid binding by an administered sequestrant, since the serum bile-acid concentration is determined largely by the rate of intestinal absorption in healthy individuals. To test this, serum bile-acid concentrations were measured at frequent intervals over 24 h in five otherwise healthy hypercholesterolaemic subjects during the ingestion of three standard meals, with or without the addition of 5 g colestipol granules administered 30 min before each meal. Total serum bile-acid concentration was measured with a previously reported bioluminescent enzymic assay, that uses a 3 alpha-hydroxysteroid dehydrogenase, an oxido-reductase, and a bacterial luciferase co-immobilized on to Sepharose beads. Bile acids in 1 ml of serum were isolated by solid-phase extraction chromatography with reversed-phase C18 cartridges. Colestipol lowered the postprandial elevation of serum bile acids by one half, with a subsequent decrease in the cumulative area under the curve. The data suggest that measurement of serum bile-acid concentrations by bioluminescence is a rapid, simple way to document the efficacy of bile-acid sequestrants.

Lyophilized Clostridium perfringens 3 alpha- and Clostridium bifermentans 7 alpha-hydroxysteroid dehydrogenases: two new stable enzyme preparations for routine bile acid analysis

Preparations of 3 alpha-hydroxysteroid dehydrogenase (EC 1.1.1.50) from Clostridium perfringens were successfully lyophilized into a stable powder form. Purification of the enzyme was achieved using triazine dye affinity chromatography. C. perfringens 3 alpha-hydroxysteroid dehydrogenase was purified 24-fold using Reactive Red 120 (Procion Red) -cross-linked agarose (70% yield). Quantitative measurement of bile acids with the purified enzymes, 3 alpha-hydroxysteroid dehydrogenase and 7 alpha-hydroxysteroid dehydrogenase (EC 1.1.1.159) from Clostridium bifermentans (strain F-6), was achieved spectrophotometrically. Standard curves with chenodeoxycholic acid (CDC) and cholic acid were linear within a concentration range of 20-100 microM. Analysis of mixtures of ursodeoxycholic acid and CDC showed the additive nature of the 3 alpha-hydroxysteroid dehydrogenase and showed also that 7 alpha-hydroxyl groups were independently quantified by the 7 alpha-hydroxysteroid dehydrogenase. Bile acids in Folch extracts of human bile samples were measured using purified preparations of Pseudomonas testosteroni 3 alpha-hydroxysteroid dehydrogenase, C. perfringens 3 alpha-hydroxysteroid dehydrogenase, Escherichia coli 7 alpha-hydroxysteroid dehydrogenase and C. bifermentans (strain F-6) 7 alpha-hydroxysteroid dehydrogenase. Statistical comparison validated the use of C. perfringens 3 alpha- and C. bifermentans 7 alpha-hydroxysteroid dehydrogenases for the quantification of bile acids in bile.

Cyclic fluctuations in fasting serum bile acid levels detected with a sensitive enzyme/bioluminescent assay

A sensitive two-step bioluminescent assay for total serum bile acids was developed using commercially available enzymes. In the first step, the bile acids present in 10 microL of alkali-treated serum were oxidised at pH 9.5 by high purity 3 alpha-hydroxysteroid dehydrogenase to form NADH. Then, NADH was quantitated at pH 6.5 under optimal conditions for bioluminescence using FMN:NADH oxidoreductase and luciferase from Photobacterium fischeri. The enzyme/bioluminescent assay correlated well with gas-liquid chromatography and radioimmunoassay methods. Assay of fasting sera in eight healthy subjects revealed cyclic fluctuations in bile acid concentrations which were inversely related to gallbladder volume. These results provide biochemical evidence for interdigestive partial gallbladder emptying as a normal physiological process.

Structural and functional integrity of rat liver perfused in backward and forward directions

The purpose of this study was to assess if reversal of the direction of isolated rat liver perfusion would cause significant alterations in hepatic functions and structure. Five isolated rat livers were perfused forward and another five backward with oxygenated Ringer's solution for up to 90 min (hydrostatic pressure: less than or equal to 13 cm H2O; flow rate: forward 3.88 +/- 0.34 ml/min per gram and backward 3.76 +/- 0.34 ml/min per gram). At the end of the experiment, livers were perfusion-fixed for morphological examination. The following results were obtained: No significant differences were noted between the forward and backward perfusions with respect to oxygen uptake, mean bile flow (forward 0.57 +/- 0.12; backward 0.60 +/- 0.14 ml/min per gram), average bile acid excretion (forward 2.39 +/- 1.11; backward 2.83 +/- 0.94 nmol/min per gram), hydroxylation pattern of bile acids, urea synthesis, release of lactic dehydrogenase, glucose secretion, and redox ratios. Light and electron microscopy, including morphometry of parenchymal and sinusoidal areas, revealed that the backward perfusion caused a greater degree of sinusoidal distension, but no other noteworthy differences. Hepatic ultrastructure was well preserved. We conclude that reversing the direction of perfusion does not alter structure and major hepatic functions significantly.

Determination of chenodiol bioequivalence using an immobilized multi-enzyme bioluminescence technique

Measurement of the bioequivalence of formulations of chenodiol, a bile acid which is used for gallstone dissolution, is difficult because its high first-pass clearance results in low plasma levels after ingestion of usual dosages. To solve this problem, a new method was developed to determine the bioequivalence of several chenodiol formulations. The method included the following steps: isolation of all bile acids from serum by absorption to a hydrophobic resin, elution of bile acids from the resin by methanol, separation of the unconjugated bile acid fraction by an ion-exchange procedure, and bioluminescence measurement of the unconjugated 7 alpha-hydroxy bile acids using Sepharose beads containing co-immobilized 7 alpha-hydroxysteroid dehydrogenase, diaphorase, and luciferase. The isolation method gave complete recovery, and the bioluminescence procedure was simple, rapid, and sensitive. The peak level of systemic chenodiol occurred 1 to 2 h following oral ingestion and ranged from 4 to 8 microM. This method appears superior to previously reported methods for determining the bioequivalence of chenodiol preparations. In principle, the method is suitable for measurement of the bioequivalence of other bile acids provided the appropriate hydroxysteroid dehydrogenase is available.

Bioluminescent assays using coimmobilized enzymes

In summary the use of immobilized luciferases along with other enzymes offers a method for measuring a wide variety of metabolites or enzymes. The assays are rapid, sensitive, and specific and can be automated. It is anticipated that many more assays for different compounds will be developed in the future.

Rapid and accurate reversed-phase high-performance liquid chromatographic determination of conjugated bile acids in human bile for routine clinical applications. Therapeutic control during gallstone dissolution therapy

This paper introduces a new method to detect the taurine and glycine conjugates of five different bile acids (cholic acid, deoxycholic acid, chenodeoxycholic acid, ursodeoxycholic acid and lithocholic acid) in human bile. Advantages of this method are sufficient separation of compounds within a short period of time and a high rate of reproducibility. Using a mobile phase gradient of acetonitrile and water, modified with tetrabutylammonium hydrogen sulphate (0.0075 mol/l), we were able to maximize the differentiation between ursodeoxycholic acid and lithocholic acid, which is of primary interest during conservative gallstone dissolution therapy. Use of this gradient reduced analysis time to less than 0.5 h. Recovery rates for this modified method ranged from 94% to 100%, and reproducibility was 98%, sufficient for routine clinical applications.

Chemistry and enterohepatic circulation of bile acids

A brief review is given of the chemistry of bile acids, emphasizing the relationship between chemical structure, physical properties and enterohepatic cycling of the major primary and secondary bile acids. Features of the enterohepatic circulation of primary and secondary bile acids in man are summarized. The effects of bile acid feeding on the composition of the enterohepatic circulation in man are reviewed. Methods for characterizing the enterohepatic circulation of bile acids in man are tabulated.