The aminopyrine demethylation breath test and the serum bile acid level: nominated but not yet elected to join the common liver tests

Clinical Pathology Approaches to Hepatic Injury

Testing the blood for evidence of hepatic damage and dysfunction frequently involves measuring several blood constituents simultaneously to screen for disease. While useful, this approach occasionally leads to apparent disparities between the blood test results, and the results of other diagnostic tests such as histology. In part, these perceived discrepancies may stem from a lack of appreciation for tissue, cellular, and molecular factors that affect the appearance of hepatic disease biomarkers in the blood. Further confusing the matter is that in some instances the mechanisms responsible for the appearance of diagnostic compounds in blood are only partially understood. Many of the known factors that affect hepatic biomarkers are similar to those affecting other tissue markers, while others are unique to the liver, such as those involved with cholestasis. Disease conditions can also cause misleading results by affecting tissue concentrations of test compounds, hepatic mass, and the clearance rate of compounds from the blood. Knowledge of the factors affecting the blood concentrations of biomarkers, as well as investigations into the mechanisms behind changes to hepatic biomarker concentrations, may allow for a better interpretation of blood test results and fewer inconsistencies between diagnostic results.

Biosynthesis of bile acids in mammalian liver

The biosynthesis of bile acids in mammalian liver and its regulation, together with the physiological role of bile acids, are reviewed in this article. Bile acids are biosynthesized from cholesterol in hepatocytes. Several steps are involved including epimerisation of the 3beta-hydroxyl group, reduction of the delta4 double bond to the 5beta-H structural arrangement, introduction of alpha-hydroxyl groups at C7 or C7 and C12 and, finally, oxidative degradation of the side chain by three carbon atoms. This gives the primary bile acids, cholic and chenodeoxycholic acids. Cholesterol-7alpha-hydroxylation is the rate determining step in the biosynthesis of cholic and chenodeoxycholic acids. Feedback regulation of cholesterol biosynthesis occurs by various mechanisms including termination of the synthesis of specific cytochromes P-450, modulation of specific cytosol proteins, short-term changes in the process of phosphorylation-dephosphorylation and changes in the capacity of the cholesterol pool as a substrate. Prior to being exported from the liver, bile acids are conjugated with glycine and taurine to produce the bile salts. After excretion into the intestinal tract, primary bile acids are partly converted to secondary bile acids, deoxycholic and lithocholic acids, by intestinal microorganisms. The majority of bile acids is absorbed from the intestinal tract and returned to the liver via the portal blood, so that only a small fraction is excreted in the feces. Bile acids returned to the liver can be reconjugated and reexcreted into the bile in the process of enterohepatic recycling. In addition to the physiological function of emulsifying lipids in the intestinal tract, bile acids are particularly important in respect of their ability to dissolve and transport cholesterol in the bile.

Pre- and postprandial total serum bile acid concentration following acute liver damage in dogs

The importance of preprandial and postprandial total bile acids were investigated in dogs with liver damage induced by carbon tetrachloride (CCl4) administration. Six healthy and mature dogs were used. After base-line clinical and biochemical examinations, hepatocellular damage was induced by oral CCl4 administration. Determinations of plasma total protein (TP), albumin (Alb), total and direct bilirubin (TBil, DBil), alanine aminotransferase (ALT) and alkaline phosphate (ALP) along with histologic examination of the livers 10 days following CCl4 administration were conducted to ensure that hepatic damage was in fact induced by the CCl4 administration. Twelve h fasting preprandial and 2 h postprandial serum total bile acids (PRSBA, POSBA) concentrations were also measured. The median plasma TP, Alb, TBil and DBil concentrations did not show any difference (P > 0.05) during the study. Plasma ALT activities increased significantly (P < 0.05, P < 0.01) between on the 3rd and 10th days of the experiment. The median serum values of PRSBA and POSBA were significantly different (P < 0.01) on the first day and continued to be different during the experiment. In conclusion, POSBA seemed to be more reliable than PRSBA in the diagnosis of hepatic necrosis.

[13C]Aminopyrine breath test detects altered liver metabolism caused by low-dose oral contraceptives

The [13C]aminopyrine breath test measures hepatic mixed function oxidase activity. The cumulative percent dose recovered over 2 hr is a sensitive indicator of hepatic dysfunction; values < or = 7.0% have been shown to indicate severe liver disease. Previous studies have suggested that the test results may be influenced by the use of oral contraceptives steroids. We compared the results from five non-oral contraceptive-using women with those from 31 women whose duration of oral contraceptive steroid usage ranged from 4 to 204 months. The women were taking one of four oral contraceptive formulations that differed in the amounts of estrogen (20, 35, or 50 micrograms with 1 mg progesterone) and progesterone (35 micrograms estrogen with stepped levels of progesterone of 0.5, 0.75, and 1.0 mg). The [13C]aminopyrine breath test was performed on days 21 and 28 of the menstrual cycle. Cumulative percent dose recovery values among the normal menstrual cycle of non-oral contraceptive steroid-using women were 12.1 +/- 1.6 and 11.8 +/- 1.5% (mean +/- SD). In contrast, oral contraceptive steroid users showed a marked reduction in cumulative percent dose recovery at 21 days, averaging 6.1 +/- 2.3% (P < 0.001), and returned to normal values (10.2 +/- 3.5%) at 28 days in most women(seven days after oral contraceptive steroid usage was paused). The adverse impact on hepatic mixed function oxidase by oral contraceptive formulations did not differ on the basis of estrogen or progesterone content. The adverse impact of oral contraceptive usage on the mixed function oxidase activity measured by the [13C]aminopyrine breath test must be considered for women of childbearing potential.

Daily determination of individual serum bile acids allows early detection of hepatic allograft dysfunction

Acute graft rejection is still a major cause of morbidity after orthotopic liver transplantation, and its diagnosis necessitates an invasive liver biopsy. Our aim has been to determine whether changes in individual serum bile acid levels after engraftment are sensitive, specific and reliable indicators of graft function and whether these changes can antedate other biochemical indicators of hepatic allograft rejection. Individual bile acids in 200 serum samples taken serially from eight adult liver transplant patients were measured. Patients with biopsy-confirmed graft dysfunction due to rejection or nonrejection causes (n = 6 episodes) had significantly higher serum concentrations of glycocholate plus glycochenodeoxycholate and taurocholate/taurochenodeoxycholate ratios than did noncomplicated grafts (n = 3). These changes antedated any other conventional biochemical parameters by at least 48 hr and were 100% sensitive and specific. None of the conventional liver function tests could match this. Acute rejection episodes (n = 3) were then compared with nonrejection causes of graft dysfunction (n = 3). In acute rejection we noted a significant increase in the concentration of glycodeoxycholate plus deoxycholate and a significant decrease in the cholate/chenodeoxycholate ratio compared with that in nonrejection graft malfunction. Both of these changes antedated any other biochemical parameters by 24 hr. In conclusion, individual serum bile acid assays, after orthotopic liver transplantation, can detect graft dysfunction resulting from any cause at an earlier time than routine biochemical tests, and they are sensitive, specific and reliable for early detection of graft dysfunction. In addition, acute rejection can be distinguished from other causes of graft dysfunction.

Assessment of lidocaine metabolite formation in comparison with other quantitative liver function tests

In clinical practice, the seriousness of liver disease is assessed based on the combined information from clinical examination, routine biochemical tests, and liver histology. Recently, the assessment of hepatic lidocaine metabolism has been proposed as a quantitative liver function test offering valuable additional information. To evaluate whether this new liver function test reflects the combined clinical assessment, we prospectively measured lidocaine metabolism in 111 patients with well characterized liver disease. In addition, lidocaine test results were compared with the aminopyrine breath test and the galactose elimination capacity. Lidocaine (1 mg/kg) was injected i.v. and serum concentrations of its main metabolite monoethylglycinexylidide were determined after 15 min. The results varied widely and the means (+/- S.D.) were similar among patients with mild liver disease (46 +/- 23 ng/ml), but significantly (P < 0.05) lower among patients with Child class A cirrhosis (19 +/- 11 ng/ml) or Child class B or C cirrhosis (21 +/- 19 ng/ml). The [13C]aminopyrine breath test, however, gave a better discrimination among patients with increasing severity of liver disease than lidocaine metabolite formation. The galactose elimination capacity finally best separated patients with mild liver disease from those with cirrhosis. The correlations between any two of the different quantitative liver function tests were weak (R2 consistently < 0.2). We conclude that lidocaine metabolite formation, like other quantitative liver function tests that are based on the microsomal metabolism of model compounds, quantitates a very particular enzymatic reaction which may not be representative for the functional reserve of the entire organ.

Aminopyrine breath test in the prognostic evaluation of patients with cirrhosis

This prospective study assessed the role of aminopyrine breath test in the prognosis of patients with cirrhosis, and evaluated whether the test provided useful information not included in the Pugh score. During a period of 36 months, 125 patients with biopsy proven liver cirrhosis were included, and followed for up to 48 months (median 17 months). During follow up 43 patients died (20 of liver failure). Survival was univariately related to aminopyrine breath test (p less than 0.02), Pugh score (p less than 0.01), presence of ascites (p less than 0.01), and sex (p less than 0.05). Using Cox's regression analysis, Pugh score, aminopyrine breath test, and sex, were independent significant predictors of survival. From the Cox's model a prognostic index was computed. According to a receiver operating characteristic curve analysis, the prognostic index predicting death showed an improvement in area under the curve when compared with a prognostic index calculated excluding aminopyrine breath test, but the improvement did not reach statistical significance (p = 0.12). A similar prognostic index was calculated to predict death from liver failure. Cox's regression analysis selected aminopyrine breath test, Pugh score, and aetiology as the best set of predictor covariates. According to a receiver operating characteristic curve analysis, a prognostic index cut off value of 2.6 had a 94% sensitivity and a 88% specificity. The prognostic index significantly improved prognostic accuracy when compared with a prognostic index calculated from Pugh score and aetiology, but excluding aminopyrine breath test (p = 0.05). These data disclose that the aminopyrine breath test offers additional prognostic information to the Pugh score, and the prognosis of patients with cirrhosis.

Analysis of the deterioration rates of liver function in cirrhosis, based on galactose elimination capacity

The prognosis of cirrhotic patients may depend on their liver function, but very few data are available to predict life expectancy in individual subjects on the basis of their liver function tests. The yearly changes in liver function, based on galactose elimination capacity (GEC), were retrospectively analyzed in 76 cirrhotic patients. The first GEC measurement had always been performed at the time of diagnosis. From that time on, mean GEC changes (in mmol/min per year) were +0.13 [SD 0.60] in the 1st year (range: +1.42/-1.35), and -0.03 [0.30] in the 2nd year (P = ns). Only after 36 months could a significant deterioration in liver function be demonstrated, but GEC changes still ranged from +0.14 to -0.35. The trend in liver function was similar in patients with alcoholic and non-alcoholic cirrhosis, but in alcoholics a favourable effect of abstinence was proved. In individual subjects, 2 consecutive GEC measurements, at least 6 months apart, failed to predict the following GEC values. The coefficients of determination between expected and measured GEC or delta GEC were 0.13 and 0.36, respectively (n = 58). When forecasting was limited to 2 years (n = 38), still only 31% and 55% of GEC values and delta GEC variance was predictable on the basis of preceding GEC values. The study shows that no definite trends in liver function deterioration rates can be observed in cirrhosis. This limits the usefulness of liver function tests in predicting prognosis in cirrhotic patients.

Role of the standard 'liver function tests' in current clinical practice

A prerequisite of current therapy in liver disease is precise diagnosis. The rapid increase in the number of tests available--immunological, virological, histological and radiological--testifies to this, and reflects the inadequacy of the 'standard' liver function tests (LFTs). The LFTs are, however, in contrast to these more sophisticated tests, observer independent and despite their lack of specificity, several characteristic patterns of abnormality can be recognised which direct the physician to the most appropriate definitive investigation. The cheapness and non-invasive nature of the LFTs makes them particularly appropriate for monitoring the course of liver diseases once the diagnosis has been established and this, together with screening for hepatotoxicity of newly developed drugs, is now their main role. A second generation of liver function tests based on the capacity of the liver to eliminate various test compounds may come closer to offering a true estimate of liver function. More accurate methods of measuring the various bilirubin fractions, particularly bilirubin conjugates may also become available in the near future and provide more sensitive tests of liver dysfunction.

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.

Immobilized bacterial luciferase and its applications

This review discusses the properties of the bioluminescent bacterial system as well as the methods for immobilization of bacterial luciferases and for their co-immobilization with other enzymes. The analytical systems using immobilized bacterial luciferases and their applications in analytical biochemistry and biotechnology have been described.

Advances in the application of biochemical tests to diseases of the liver and biliary tract: their role in diagnosis, prognosis, and the elucidation of pathogenetic mechanisms

Despite the biochemical complexity of the liver, few laboratory tests provide discriminatory diagnostic information in patients with hepatobiliary disease. Recent efforts have concentrated upon tests which assess the function of the liver, the severity of the disease state, and underlying pathological processes. Bile Acids: The emergence of facile technology and widespread application has brought the realization that these assays are not as sensitive in detecting liver disease as previously believed, although the cholate/chenate ratio may be useful in distinguishing cholestasis from chronic liver disease. The presence of unusual bile acids in serum or urine may be helpful in some cases. Drug Metabolism: A number of tests provide good evidence about liver function, hepatic blood flow and portal shunting, but the aminopyrine breath tests is the most useful, giving prognostic information in acetaminophen overdose and alcoholic liver disease. The antipyrine half-life identifies surgical cases at risk from poor hepatic function. Proteins and Immunochemical Tests: Interest has developed in plasma proteins such as prealbumin and retinol-binding protein to monitor hepatic protein synthetic function. Secretory IgA is more elevated in biliary tract disease, unlike the native protein which is increased principally in cirrhosis. Type III procollagen can be measured in serum, and correlates with the activity of collagen synthesis and the degree of fibrosis in biopsy samples. Reye's Syndrome: Biochemical tests play an essential role in diagnosis of this recently discovered disease. These will be presented and discussed.

Diagnostic sensitivity of fasting and postprandial serum bile acids determined by different methods

The diagnostic sensitivities of serum bile acids determined by three different methods in the fasting and in the postprandial state were compared in 43 patients with cirrhosis of the liver. When a method with high analytical sensitivity (capillary gas-liquid chromatography, GLC, or radioimmunoassay, RIA) was used, the serum concentrations of bile acids exhibited similar diagnostic sensitivities in the fasting state (GLC, 98%; RIA, 93%) and in the postprandial state (GLC, 95%; RIA, 93%). By contrast, when an enzymatic method with limited analytical sensitivity was employed, the diagnostic sensitivity of fasting serum bile acids was lower (79%) than that of postprandial serum bile acids (93%). The measurement of individual serum bile acids by GLC did not add any further diagnostic information. The results of this study demonstrate that the diagnostic sensitivity of serum bile acids strongly depends on the analytical method used.

A review of new approaches to assessing hepatic function in animals

Although a multitude of effective liver function tests are available for use in animals, a variety of modifications of currently used tests have been recently reported. In addition, newer procedures now used in human medicine may also provide unique insights into assessing and detecting acquired hepatic disorders in animals. Examples of new procedures are: assessing microsomal mixed function oxidase activity by plasma caffeine clearance; estimating the extent of active hepatic fibrogenesis through serum procollagen-III peptide levels; determining hepatic blood flow and functional mass by the galactose elimination capacity; detecting primary hepatocellular cancer through serum or urinary ligandin levels; and to estimate the liver's maximal capacity to excrete indocyanine green independent of blood flow. In evaluating drugs as to their hepatotoxicity, function tests should be included in the liver profile which measure specific metabolic alterations unique to the compound under study.

Decreased uptake of taurocholate and ouabain by hepatocytes isolated from cirrhotic rat liver

To differentiate between the "intact" and "sick" cell hypothesis explaining decreased clearance of endo- and xenobiotics, we measured uptake of taurocholate and ouabain in hepatocytes isolated from cirrhotic rat liver. Cirrhosis was induced by chronic exposure of male Sprague-Dawley rats to phenobarbital and carbon tetrachloride. Uptake of [14C]taurocholate and [3H]ouabain was measured by a rapid filtration technique. Hepatocytes from cirrhotic liver were as viable as control hepatocytes--as judged by trypan blue exclusion and lactate dehydrogenase release--but consumed 28% less oxygen. Vmax of both taurocholate (3.16 +/- 0.95 vs. 0.40 +/- 0.35 nmoles X min-1 X 10(6) cells-1; p less than 0.001) and ouabain (2.16 +/- 0.78 vs. 0.83 +/- 0.26 nmoles X min-1 X 10(6) cells-1; p less than 0.005) was significantly reduced. These results are compatible with the "sick" cell hypothesis.

Prognostic value of the aminopyrine breath test in cirrhotic patients

The aminopyrine breath test has been proposed as a quantitative test of hepatic function, but its long-term prognostic value in patients with cirrhosis has not been determined. The aim of this study was to examine the usefulness of the aminopyrine breath test in assessing prognosis and to compare it with traditional methods of evaluating liver function. One-hundred eighty-seven patients with histologically confirmed cirrhosis were studied prospectively. An aminopyrine breath test was obtained at the time of inclusion in the study and results were expressed as per cent of the dose excreted in 2 hr. At inclusion, the severity of liver disease was also assessed according to the Pugh modification of the Child-Turcotte classification based on ascites, neurological status, serum albumin, serum bilirubin and prothrombin time. Mean follow-up was 844 days. During that period, 59 of 187 patients died of their liver disease. Two-year survival decreased with increasing Child-Turcotte classification score: survival was 98% in Child Class A patients (n = 62), 66% in Child Class B (n = 76) and 36% in Child Class C (n = 49) (chi 2 = 65.6, p less than 0.001). Two-year survival also decreased significantly with increasing degree of aminopyrine breath test abnormalities: survival was 90% in patients with aminopyrine breath test greater than 4% (n = 56); 78% in patients with aminopyrine breath test = 2 to 4% (n = 66), and 43% in patients with aminopyrine breath test less than 2% (n = 65) (chi 2 = 36.9, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative liver function in the elderly assessed by galactose elimination capacity, aminopyrine demethylation and caffeine clearance

Hepatic function was assessed in 13 healthy elderly subjects, 71-88 years of age, with three quantitative tests of liver function. The galactose elimination capacity was significantly (P less than 0.05) lower in the elderly (6.08 +/- 1.30 mg X min-1 X kg-1, mean +/- SD) than in a group of 70 subjects under 40 (7.48 +/- 0.94 mg X min-1 X kg-1) and 11 subjects between the age of 40 and 70 (7.08 +/- 0.68 mg X min-1 X kg-1). The demethylation of aminopyrine as assessed by the aminopyrine breath test, and the systemic clearance of caffeine, two measures of microsomal function, demonstrated a comparable decrease but showed much more interindividual variation. Caffeine clearance decreased from 1.49 +/- 0.44 ml X min-1 X kg-1 in young adults to 0.97 +/- 0.39 ml X min-1 X kg-1 (P less than 0.01) in the elderly, and the demethylation of aminopyrine decreased from 0.79 +/- 0.15 to 0.62 +/- 0.20% dose X kg X mmol-1 (P less than 0.05). Our data indicate that aging is associated with a loss of the functioning mass of hepatocytes. The decrease in drug metabolism parallels the loss of functional mass but shows more interindividual variation probably reflecting the many genetic and environmental factors influencing these tests of microsomal function.

Evaluation of the diagnostic value of serum bile acid in the detection and functional assessment of liver diseases

The diagnostic usefulness of fasting total serum bile acids (SBA/F) in the detection of liver diseases and assessment of different aspects of hepatic function alteration was evaluated in 61 healthy subjects and 186 patients with liver disease. The value of SBA/F was compared with other routine tests. In 49 healthy subjects and 92 patients, serum bile acids were also measured after the im administration of Ceruletide as a cholecystokinetic agent (SBA/C). The diagnostic efficacy for the detection of disease states was better with aspartate-aminotransferase (EC 2.6.1.1) and alanine-aminotransferase (EC 2.6.1.2) than with SBA/F. When SBA/C was also determined the diagnostic efficacy was not substantially better than the SBA/F test. In the assessment of hepatocellular necrosis SBA/F showed a higher rate of misclassification errors compared to alanine-aminotransferase (mean error 45% vs 17%), whereas SBA/F gave similar results with direct bilirubin and pseudocholinesterase (EC 3.1.1.8) in the evaluation of cholestasis (mean error 40% vs 41%) and impaired biosynthesis (mean error 39% vs 40%), respectively. Serum bile acid determination did not show any significant diagnostic advantage with respect to the other routine liver tests.

Total serum bile acids and the bile acid profile as tests of liver function

Total serum bile acid assay for the evaluation of liver function has been available for many years but its application has been limited primarily by factors such as methodology, equipment and cost. New and improved methods for bile acid assay such as the radioimmunoassay or the hydroxysteroid dehydrogenase techniques have brought the assay for bile acids into the realm of the clinical laboratory. The efficacy of bile acids for clinical diagnostic use in the evaluation of liver function has not been firmly established. Newer methods using high pressure liquid chromatography to develop a profile of the different bile acids may clarify its usefulness and define its role among the many available tests of liver function in animals.

The diagnostic value of fasting individual serum bile acids in anicteric alcoholic liver disease: relation to liver morphology

The aim of the present study was to evaluate the diagnostic value of measuring individual serum bile acids in patients with suspected alcoholic liver disease. A highly accurate and specific mass-fragmentographic technique with high sensitivity was used. Anicteric patients with fatty liver (n = 10) and liver cirrhosis (n = 9) were compared with healthy controls (n = 27). The measurement of serum bile acids did not discriminate patients with fatty liver from controls. In general, an increased serum level of cholic acid indicated more serious liver disease. Determination of chenodeoxycholic acid and deoxycholic acid did not add any further diagnostic information.

Fasting serum bile acid level in cirrhosis. A semi-quantitative index of hepatic function

We examined the roles of the factors which influence bile acid levels in order to define to what extent fasting serum total bile acid (FSTBA) level might reflect hepatic function and/or anatomy of the portal circulation in patients with cirrhosis. In a first group of 13 patients having mild to moderately advanced cirrhosis we determined the apparent oral clearance (CLo) of chenodeoxycholic acid (764 mumol) and their FSTBA levels. In a second group of 15 similar patients we measured FSTBA levels and by hepatic vein catheterization the intrinsic clearance (CLi) of ICG as well as total hepatic blood flow (Q). We found a significant inverse log-log relationship (r = 0.752, P less than 0.01) between the FSTBA and the CLo on the one hand and significant inverse log-log relationship (r = 0.707, P less than 0.01) between the FSTBA and CLi on the other hand. Q was not found to bear any significant relation to FSTBA (r = 0.120, P greater than 0.1). To conclude, in view of the observed relationship between CLi and CLo vs FSTBA, the latter might serve as a simple non-invasive semiquantitative index of hepatic function and/or anatomy of portal circulation in cirrhosis.

Bioluminescence assays for bile acids in the detection and follow-up of experimental liver injury

We evaluated the usefulness of recently developed bioluminescence assays for serum bile acids (BA) in the detection and follow-up of experimental liver injury. Liver damage was induced in rats by either D-galactosamine or CCl4, and BA were compared to SGPT and aminopyrine breath test (ABT). In severe liver injury, following D-galactosamine administration, all three methods revealed a significant difference from control values. The degree of abnormality was, however, far greater with SGPT and BA than with ABT. In moderate liver injury, induced by CCl4, the increase in BA was not significant. Values of SGPT and BA showed a very good correlation (3 alpha-OH: r = 0.88; 7 alpha-OH: r = 0.90; 12 alpha-OH: r = 0.83; p less than 0.001 for all correlations). Application of different assays for 3 alpha-OH, 7 alpha-OH and 12 alpha-OH BA allowed us to assess changes in individual BA. A 96-hr follow-up study in D-galactosamine-treated animals showed an increase in BA up to 48 hr and a decrease thereafter. The bioluminescence assays for BA are simple, rapid and require only 10 microliter of serum. Thus, these assays may be the method of choice in detecting and monitoring liver injury in small laboratory animals.

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

A bioluminescence assay for bile acids was developed using a co-immobilized 3 alpha-hydroxysteroid dehydrogenase, diaphorase, and bacterial luciferase. The assay was specific for bile acids containing a free 3 alpha-hydroxyl group, as well as androsterone. Light output was linear over a bile acid concentration range of 1-20 000 pmol. Intra-assay precision was 6.2-8.2% and the recovery of added standards was 92-110%. Comparison of results using the bioluminescence assay with those using gas liquid chromatography revealed an excellent correlation (r = 0.99, n = 31). Since the bioluminescence assay is rapid, sensitive, specific, and uses inexpensive reagents, it appears to be an ideal method for the measurement of total bile acids in serum.

Caffeine: a model compound for measuring liver function

The effects of liver disease on caffeine plasma clearance (Cl) and on exhalation of 14CO2 following i.v. injection of 2 mu Ci of [3-methyl-14C]caffeine together with 125 mg of the unlabeled compound were measured in 15 patients with cirrhosis, 11 subjects with miscellaneous liver disease, and 10 normal volunteers. Compared to mean values for Cl (2.02 +/- S.D. 0.68 ml per min per kg) and t1/2 (3.8 +/- 0.9 hr) in normal volunteers, cirrhotics were characterized by highly significant reductions in Cl (to 0.76 +/- 0.40) and prolongation in t1/2 (to 13.7 +/- 13.0), whereas the volume of distribution (VD) remained relatively unchanged (0.57 +/- 0.16 vs. 0.64 +/- 0.13 liter per kg in normals). Cumulative 14CO2 production and specific activity of 14CO2 in breath decreased in parallel (r = 0.83) with Cl. Patients with miscellaneous liver disease exhibited only small changes in Cl and t1/2; however, 14CO2 parameters in breath appeared more sensitive in indicating the slight functional derangement. In view of the correlation (Rs = 0.83) of cumulative 14CO2 excretion with the initial disappearance constant for bromosulfophthalein, the caffeine breath test may be considered as a quantitative measure of hepatic microsomal activity; based on a surprisingly close, hyperbolic relationship between Cl and fasting caffeine plasma concentrations, the latter might serve as a simple guide to severity of liver disease.

A bioluminescent assay for 12-alpha-hydroxy bile acids using immobilized enzymes

A bioluminescent assay for 12-alpha-hydroxy bile acids was developed using enzymes coimmobilized onto Sepharose 4B. The immobilized enzymes used were a bacterial 12-alpha-hydroxysteroid dehydrogenase, bacterial luciferase, and NADPH:FMN oxidoreductase or bacterial diaphorase. The assay was specific for 12-alpha-hydroxy bile acids and the lower limit of detection was 4 pmol/0.5 ml assay volume with a linear range of 4 to 2000 pmol. Intraassay precision was from 7.8 to 8.2%. Values obtained with this assay showed good agreement with those obtained by gas-liquid chromatography. The system using diaphorase was not stable at 4 degrees C in the absence of added thiol compounds, but could be stabilized by the addition of glutathione (0.5 mM). The assay is a convenient, a rapid, and an extremely sensitive method for the measurement of 12-alpha-hydroxy bile acid concentrations in the serum of patients or experimental animals.