Determinants of fasting and postprandial serum bile acid levels in healthy man

The relationship between serum levels of conjugates of cholic acid measured by radioimmunoassay, bile acid absorption, and hepatic clearance was studied in order to define the determinants of fasting and postprandial serum bile acids in healthy man. Acute or chronic interruption of the enterohepatic circulation caused a significant decrease in basal serum levels of cholyl conjugates, while liquid or solid meals caused a marked and reproducible increase in serum cholyl conjugates. A temporal correlation was demonstrated postprandially or after intravenous cholecystokinin between intestinal transit of bile acids and simultaneous changes in levels of serum cholyl conjugates. Finally, the plasma disappearance of intravenously injected cholylglycine was shown to be unaffected by serum levels of endogenous cholyl conjugates. These data are consistent with the interpretation that, in the presence of normal hepatic function, the major determinant of serum bile acids is their rate of intestinal absorption.This work was supported by Mayo Foundation and USPHS Grant AM 16770.A part of this work was presented at the 1975 meeting of the American Association for the Study of Liver Disease and published in abstract form (1). Dr. Hoffman's present address is: Division of Gastroenterology, Department of Medicine, University of Texas, Houston, Texas. Dr. Korman's present address is: Department of Medicine, Monash University, Prince Henry's Hospital, Melbourne, Australia. Dr. Cowen's present address is: Department of Medicine, Royal Brisbane Hospital, Queensland, Australia.     

Diagnostic value of serum primary bile acids in detecting bile acid malabsorption.

Serum cholic and chenodeoxycholic acid conjugates were measured in fasting conditions and after meals in 14 patients with bile acid malabsorption due to ileal resection. Mean serum fasting levels of both primary bile acids did not differ from the controls. After meals, serum cholic acid peaks were lower in patients with ileal resection than in control subjects (p less than 0.001), while chenodeoxycholic acid peaks were reduced in colectomised patients (p less than 0.01). In the sera from patients with ileal resection, the glycine/glycine + taurine ratio for cholic and chenodeoxycholic acid increased (p less than 0.001) from morning to evening, and glycine/glycine + taurine ratio for chenodeoxycholic acid was significantly (p less than 0.01) different from the controls in the sera collected in the evening. The results are consistent with the concept of a better intestinal conservation of chenyl, mainly of the glycine conjugated from, than of cholylconjugates, in patients with ileal resection; this is probably because of passive absorption in the intestine. The postprandial peaks of serum cholic acid conjugates may therefore be regarded as a test of ileal dysfunction, while peaks of chenodeoxycholic acid conjugates suggest colonic impairment.     

Bile acid malabsorption

Opinion statement Patients with bile acid malabsorption typically present with chronic, watery diarrhea. Bile acids recirculate between the liver and small intestine in the enterohepatic circulation. They are reabsorbed in the distal small intestine, and normally only a small fraction of the bile acid pool is lost to the colon during each cycle. In patients with bile acid malabsorption, a larger amount of bile acids is spilled into the colon, where the acids stimulate electrolyte and water secretion, which results in loose to watery stools. The common causes of bile acid malabsorption are ileal resection and diseases of the terminal ileum (Crohn’s disease and radiation enteritis), which result in a loss of bile acid transporters and, consequently, diminished reabsorption. Bile acid malabsorption also has been documented in a small group of patients with chronic, watery diarrhea who have no demonstrable ileal disease (idiopathic bile acid malabsorption). The amount of bile acid loss to the colon determines the clinical presentation. Patients with mild to moderate bile acid malabsorption present with watery diarrhea and generally respond very well to treatment (with abolishment of diarrhea) with bile acid binders such as cholestyramine. Patients with more severe bile acid malabsorption have both diarrhea and steatorrhea. Treatment with cholestyramine is of no benefit in this group of patients and may, in fact, worsen steatorrhea. These patients are best treated with a low-fat diet supplemented with medium-chain triglycerides.     

Enterohepatic circulation of bile acids after cholecystectomy.

Bile acid metabolism was investigated in 10 patients after cholecystectomy, 10 gallstone patients, and 10 control subjects. Diurnal variations of serum levels of cholic and chenodeoxycholic acid conjugates were not abolished by cholecystectomy. Cholic acid pool size was significantly reduced in cholecystectomised patients and the fractional turnover rate and the rate of intestinal degradation of bile acid showed a significant increase. In cholecystectomised patients fasting bile was supersaturated in cholesterol, though less than in gallstone patients, but, in both, feeding resulted in improvement of cholesterol solubility in bile. These data suggest that after cholecystectomy the small intestine alone acts as a pump in regulating the dynamics of the enterohepatic circulation of bile acids and that the improvement of cholesterol solubility in bile is due to a more rapid circulation of the bile acid pool in fasting cholecystectomised patients.     

Composition of biliary lipids and kinetics of bile acids after cholecystectomy in man

Postcholecystectomy biliary lipid composition and bile acid kinetics were studied in 24 women and 4 men. Hepatic bile was collected periodically for as long as 4 months without interrupting the enterohepatic circulation and without infecting the biliary system. In 23 patients with cholesterol gallstones, fasting biliary cholesterol made up 10.2% of total lipids in the steady state; in 5 patients with bilirubinate stones, saturation of fasting hepatic bile with cholesterol was lower (8.7% of total lipids). The percentage of deoxycholic acid after cholecystectomy was not higher than that of seven healthy, noncholecystectomized controls. Postcholecstectomy studies of diurnal variation of biliary lipids (7 patients) showed that postprandial hepatic bile had a significantly lower cholesterol saturation than fasting bile. Pool sizes of cholic and chenodeoxycholic acids were low (average 0.4 g/70 kg, each); total synthesis for both bile acids was normal (average 460 mg/day/70 kg), but fractional turnover rates of the two primary bile acids increased after cholecystectomy, probably due to more frequent recycling of the small bile acid pool.     

Altered fecal bile acid pattern in patients with inflammatory bowel disease

Alterations of the enterohepatic circulation of bile acids in patients with Crohn's disease (CD) and ulcerative colitis (UC) are known, but fecal bile acid patterns are less well defined. In this study total and individual fecal bile acids of 10 patients with CD (8 patients without bowel resection) 6 patients with UC and 5 healthy volunteers (HV) were determined by capillary gas chromatography. In comparison to HV (782 + 82 mg) the daily fecal excretion rate of bile acids was increased in CD (2,739 +/- 877 mg) and decreased in UC (409 +/- 55 mg). CD (80 +/- 19%) and UC (83 +/- 7%) had mainly primary bile acids, while secondary bile acids were predominant (80 +/- 4%) in HV. Bacterial conversion from primary to secondary bile acids is likely to be altered by rapid mouth-anus transit time (52 +/- 21 min) in UC and in CD by acidic stool pH (5.2 +/- 0.5). This lack of intestinal secondary bile acids may have pathophysiologic significance.     

High concentration and retained amidation of fecal bile acids in patients with active ulcerative colitis

Fecal bile acid profiles of 14 patients with ulcerative colitis in the active phase were analyzed to study the potential significance of bile acids in the pathophysiology of this disease, and the results were compared with those in 12 healthy controls. The excretion levels of total bile acids (mean +/- SD) in patients were higher than in controls, 445.1 +/- 392.1 vs 215.5 +/- 148.0 mumol/day, 3.1 +/- 1.7 vs 1.6 +/- 1.0 mumol/g wet feces (P less than 0.05), and 17.2 +/- 9.2 vs 12.4 +/- 13.3 mumol/g dry feces. Fecal profiles of individual bile acids showed higher levels of primary bile acids (52 +/- 27%) in patients compared to those (26 +/- 21%) in controls. Proportions of glycine and taurine conjugates in patients (26 +/- 24%) were higher than in controls (5 +/- 2%) (P less than 0.05), whereas proportions of unconjugates and sulfates were lower in patients than in controls. Accordingly the extent of deconjugation and dehydroxylation of bile acids was lower in patients than in controls. These trends were prominent in patients with more severe disease activity. A high concentration of bile acids in the intestine may have a significant role in the pathophysiology of ulcerative colitis at active phase.     

Regulation of bile acid synthesis. I. Effects of conjugated ursodeoxycholate and cholate on bile acid synthesis in chronic bile fistula rat

Bile acid synthesis is thought to be regulated by a negative feedback mechanism which is presumably dependent upon the flux of bile acids in the enterohepatic circulation. To characterize further the role of bile acids in regulation of bile acid synthesis, we have administered pure taurine or glycine conjugates of ursodeoxycholic acid or cholic acid to chronic bile fistula rats by continuous intraduodenal infusion, thus simulating restoration of the enterohepatic circulation. The effects of these bile salt infusions on bile acid synthesis, biliary cholesterol and phospholipid secretion and on the activities of the hepatic microsomal enzymes cholesterol 7 alpha-hydroxylase and HMG-CoA reductase were evaluated. Because the rate of biliary bile salt secretion in rats with intact exteriorized enterohepatic circulation averaged 27.1 +/- 1.4 mumoles per 100 gm rat per hr, infusion rates for bile fistula studies were chosen to match (24 to 36 mumoles per 100 gm rat per hr) or exceed (48 mumoles per 100 gm rat per hr) this physiological flux. Infusion of tauroursodeoxycholic acid for 48 hr at 24 and 48 mumoles per 100 gm rat per hr failed to suppress cholic acid synthesis. Bile flow and biliary cholesterol and phospholipid secretion exhibited small, dose-dependent increases with tauroursodeoxycholic acid infusions. No suppression of cholesterol 7 alpha-hydroxylase or HMG-CoA reductase activity was observed. By contrast, taurocholic acid inhibited synthesis of chenodeoxycholate and its metabolites alpha- and beta-muricholate by 10% (NS), 66% (p less than 0.05) and 75% (p less than 0.05) at infusion rates of 24, 36 and 48 mumoles per 100 gm rat per hr, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pancreatic carboxypeptidase hydrolysis of bile acid-amino conjugates: selective resistance of glycine and taurine amidates

To find a possible explanation for the selective hepatic conjugation of bile acids with glycine or taurine, the N-acyl amidates of cholic acid and a number of amino acids and amino acid analogues were synthesized, and their susceptibility to hydrolysis by pancreatic juice, gastric juice, serum, or small intestinal mucosal enzymes was measured. Deconjugation by pure carboxypeptidase A and B was also examined, and hydrolysis by these tissue fluids and enzymes was compared with that mediated by a bacterial cholylglycine hydrolase. Human pancreatic juice efficiently hydrolyzed cholyl conjugates of all neutral-L-amino acids (cholyl-L-alanine, cholyl-L-valine, cholyl-L-leucine, and cholyl-L-tyrosine), except cholylglycine. The net hourly rate of hydrolysis (in micromoles per milligram protein per hour) increased when the terminal residue was aromatic or branched aliphatic, and appeared to be specific for L-alpha-amino acids as cholyl-beta-alanine and cholyl-D-valine were not cleaved. From cholyl glycylglycine, only the terminal glycine was efficiently removed. Cholyltaurine and cholyl conjugates with the methyl and propyl analogues of taurine were resistant to hydrolysis. Two basic amino acid conjugates (cholyl-L-lysine and cholyl-L-arginine) were cleaved, whereas conjugates of acidic amino acids (cholyl-aspartate and cholyl-cysteate) were not cleaved. Studies using pure enzymes showed that bovine carboxypeptidase A hydrolyzed the cholyl conjugates of the neutral L-alpha-amino acids with similar specificity as observed for the human pancreatic juice, whereas bovine carboxypeptidase B cleaved the basic amino acid conjugates. Cholyl-L-lysine and cholyl-L-arginine were also cleaved by serum and plasma, which are known to possess carboxypeptidase activity. Cholyl conjugates were not cleaved by gastric juice, by trypsin, or by homogenates of rat small intestinal mucosa. In contrast, all cholyl conjugates were cleaved by a bacterial cholylglycine hydrolase. These experiments indicate that glycine and taurine amidates of cholic acid differ from a number of other conjugates with neutral and basic amino acid in being resistant to hydrolysis by pancreatic and plasma carboxypeptidases.(ABSTRACT TRUNCATED AT 400 WORDS)     

Serum bile acid concentration after a test meal.

Total serum bile acid concentrations were studied by an enzymatic-fluorimetric method employing a highly purified 3 alpha-hydroxysteroid dehydrogenase. In 28 control subjects mean total serum bile acid concentration was 2.5 mumoles/1 (S.D. 1.4). In 6 healthy subjects a significant postprandial increase in total serum bile acids occurred with maximal values at 90 and 120 minutes after ingestion of a liquid test meal. The maximal postprandial increase for each subject was 1.5 to 3 times the fasting value. In 7 patients with various hepatobiliary diseases the maximal postprandial elevation of serum bile acids was higher than in the normals, and the duration of serum bile acid elevation was significantly prolonged. In the patients with normal fasting concentration of bile acids the postprandial elevation was also significantly greater than in the controls. A 2-hour postprandial sample seems suitable for the study of the bile acid test meal response for clinical use.     

Postprandial Serum Bile Acids in Resected and Non-Resected Patients with Crohn's Disease

Fasting and postprandial serum conjugates of cholic acid (CCA) and chenodeoxy-cholic acid (CCDA) were determined by radioimmunoassay in 46 healthy individuals and 15 patients with Crohn's disease (CD), 7 bowel-resected and 8 non-resected. All patients had normal conventional liver test results, and fasting values of CCA and CCDA were within the reference ranges. Two findings appeared: the mean postprandial increases in CCA and CCDA were both lower in CD patients than in healthy individuals, and the postprandial increase in CCA was lower in the resected patients than in the non-resected, whereas the postprandial increase in CCDA was the same in the resected and the non-resected patients. These findings show that in CD patients, whether resected or not, the postprandial levels of bile acids are low. This could reflect a decreased absorptive capacity of bile acids in the small intestine. The finding that postprandial CCA, but not CCDA, was lower in resected than in non-resected patients may reflect different sites of CCA and CCDA absorption.     

Abnormal hepatic sinusoidal bile acid transport in an Amish kindred is not linked to FIC1 and is improved by ursodiol

BACKGROUND & AIMS: The mechanism for abnormal hepatic bile acid transport was investigated in an 18-month-old Amish boy who presented with pruritus, poor growth, and severe bleeding episodes. Serum bilirubin, gamma-glutamyltranspeptidase, and cholesterol levels were normal, but prothrombin time and partial thromboplastin time were prolonged and bone alkaline phosphatase level was elevated. METHODS AND RESULTS: Cholic acid plus chenodeoxycholic acid levels measured by capillary gas-chromatography were 32 times higher than control in serum (34.7 vs. 1.1+/-0.4 microg/dL) but were not detected in liver and were reduced in gallbladder bile. Treatment with ursodiol, a more hydrophilic bile acid, improved pruritus, produced 37% weight gain, and after 2 years reduced serum primary bile acid concentrations about 85%, while accounting for 71% of serum and 24% of biliary bile acid conjugates. On ursodiol therapy, hepatic bile acid synthesis was enhanced 2-fold compared with controls, and microscopy revealed chronic hepatitis without cholestasis. Three younger sisters with elevated serum bile acids responded positively to ursodiol. Microsatellite markers for the FIC1 (gene for Byler's disease) region in these 4 children were inconsistent with linkage to FIC1. CONCLUSIONS: Conjugated cholic acid and chenodeoxycholic acid were synthesized in the liver and secreted into bile but could not reenter the liver from portal blood and accumulated in serum. In contrast, unconjugated ursodiol entered the liver and was conjugated and secreted into bile. Thus, the enterohepatic circulation of all conjugated bile acids was interrupted at the hepatic sinusoidal basolateral membrane. Unconjugated ursodiol bypassed the hepatic uptake block to enlarge the biliary and intestinal bile acid pools. A mutation in FIC1 recognized among the Amish and linkage of the disorder to FIC1 were excluded.     

Do bile acids exert a negative feedback control of cholecystokinin release?

The influence of intraduodenal bile deficiency due to chronic bile duct obstruction and acute exogenous administration of bile acids on plasma cholecystokinin (CCK) and pancreatic polypeptide (PP) was investigated. Fourteen patients with tumor-induced bile duct stenosis and five healthy volunteers were given a liquid test meal. Four of the patients had a simultaneous pancreatic duct stenosis. On another day 4 g chenodeoxycholic acid were administered concomitantly with the liquid test meal in six of the patients and all controls. Basal and meal-stimulated plasma CCK did not differ between patients and controls. A pancreatic duct stenosis, which was associated with diminished plasma PP concentrations, had no influence on plasma CCK release. Exogenous bile acids significantly reduced the postprandial CCK response in both groups. Bile-induced inhibition was significantly greater in patients than in controls (75 +/- 7% and 44 +/- 11%, respectively; p less than 0.05). It is concluded that intraduodenal bile is an important modulator of the postprandial secretory activity of the CCK cell. Although chronic intraduodenal bile acid reduction in tumor-induced biliary duct stenosis did not influence plasma CCK levels, a negative feedback control of plasma CCK by acute bile acid administration could be demonstrated.     

Ursodeoxycholic acid ingestion after ileal resection

The effect of ursodeoxycholic acid ingestion on biliary bile acids and biliary lipids was studied in six patients after ileal resection. All patients had bile acid malabsorption, as documented by increased breath and fecal excretion of¹⁴C after oral administration of [1-¹⁴C] cholylglycine. Fasting duodenal bile was collected by intubation before and seven days after ursodeoxycholic acid administration (4 g/day), and biliary bile acid and lipid composition were determined. Ursodeoxycholic acid ingestion increased the percentage of ursodeoxycholic acid in bile tenfold (3.6±2.6% vs 38.6±12.0%) and decreased chenodeoxycholic acid in bile by approximately 40%. Before ursodeoxycholic acid ingestion, bile was supersaturated in all patients. After ursodeoxycholic acid ingestion, cholesterol saturation decreased in all six patients by an average of 43%, and bile became unsaturated in five. Ursodeoxycholic acid ingestion had no effect on stool frequency. We conclude that, as in subjects with an intact enterohepatic circulation, ursodeoxycholic acid therapy has litholytic potential in patients after ileal resection.This work was supported by NIH Grants AM 15887 and RR 585 and by the Mayo Foundation. Part of this work was reported at the 1979 meeting of the American Gastroenterological Association and published in abstract form.At the time this work was done, Dr. LaRusso was a Teaching and Research Scholar of the American College of Physicians.     

Diagnostic effectiveness of serum bile acids in liver diseases as evaluated by multivariate statistical methods

The aims of this study were to determine the diagnostic effectiveness of fasting and postprandial serum bile acid determinations in liver diseases, and to compare results with those of conventional liver function tests. In 322 patients with biopsy-proved liver disease and 93 healthy subjects, fasting and postprandial (2 hr) serum levels of cholic, chenodeoxycholic, and lithocholic acid conjugates and conventional liver function tests were evaluated. Data were subjected to variance and discriminant and factor analyses. Fasting serum bile acids were higher in patients when compared to controls and were significantly higher in severe than in mild liver diseases. Determination of cholic plus lithocholic acid provided the highest discrimination capacity. The percent of correct allocation was 75.4% for conventional liver function tests, 70.1% for fasting serum bile acids and increased to 79.6% when liver function tests plus serum bile acids were considered. Postprandial percentages were always lower than fasting. Factor analysis identified two factors possibly related to cytolysis and protein synthesis. The serum bile acid concentrations highly correlated with both factors. We conclude that serum bile acid determinations increase the diagnostic and discriminant capacities of liver function tests and are more sensitive and discriminant when obtained in fasting than postprandially.     

Bile acid malabsorption in HIV infected patients with chronic diarrhoea

Aims: To look for the presence of bile acid malabsorption in HIV infected patients with chronic diarrhoea and determine whether bile sequestering agents may have a role in palliating this common problem.
Methods: Nineteen HIV infected patients with chronic diarrhoea (duration >one month) poorly controlled on conventional treatment were investigated using the seven day retention of ⁷⁵seleno-23-homocholic acid taurine (SeHCAT) as a measure of bile acid loss from the enterohepatic circulation. Patients with evidence of bile acid malabsorption were offered cholestyramine.
Results: Sixteen (84%) had evidence of bile acid malabsorption (<15% retention at seven days). Ten of the 16 patients with bile acid malabsorption had terminal ileal biopsies -six had ileitis and four normal histology, suggesting that malabsorption is not always related to terminal ileitis. Thirteen patients with bile acid malabsorption have been treated with cholestyramine and 11 have reported a symptomatic response.
Conclusions: Bile acid malabsorption can be demonstrated in some cases of HIV associated chronic diarrhoea and we suggest a therapeutic trial of a bile sequestering agent in patients whose symptoms are not well controlled using conventional anti-diarrhoeal agents.     

Comparison of maximal postprandial serum cholylglycine concentration with the retention of 75Se-homotaurocholic acid in ileal dysfunction

The retention of 75Se-homotaurocholic acid (75SeHCAT) was measured in 12 healthy controls and in 21 patients with Crohn's disease and compared with the maximum postprandial rise in the serum concentration of cholylglycine (CG) in order to detect bile acid malabsorption. The retention of 75SeHCAT was lowered in all patients with inflammation or resection of the terminal ileum over a length more than 20 cm. In 64% of these patients bile acid malabsorption could also be detected by the absence of a significant rise of the postprandial CG serum level but only if the loss of the ileal function exceeded 30 cm. Although less sensitive than the 75SeHCAT retention, the CG method is simpler to apply in terms of laboratory technology and does not involve exposure to radioactivity. The CG method appears to be of use to detect bile acid malabsorption in certain cases. In the case of negatively if still bile acid malabsorption is suspected more sensitive tests such as 75SeHCAT retention should be carried out to further evaluate bile acid malabsorption.     

Effect of cholestyramine treatment on biliary lipid secretion rates in normolipidaemic men

This study was designed to clarify the effect of bile acid sequestrant treatment on the total biliary output rates of cholesterol, phospholipids and bile acids in man, and to correlate these changes with the alterations in plasma lipoprotein levels. For this purpose nine healthy, normolipidaemic men were treated with 16 g of cholestyramine daily over a period of 4 weeks, and the biliary secretion rates were measured by a duodenal perfusion technique. Resin therapy, which profoundly increases de novo synthesis of bile acids, resulted in a lowering of total plasma cholesterol levels, mainly due to a 35% reduction in low density lipoprotein (LDL) cholesterol, and in a 33% increase in plasma triglyceride levels, reflecting enhanced very low density lipoprotein (VLDL) triglyceride concentrations; high density lipoprotein (HDL) levels did not change. However, these lipoprotein changes did not correlate with any alterations in biliary lipid output. Total hepatic secretion rates of the biliary lipids remained generally unchanged during treatment, with a tendency towards lower cholesterol output, resulting in a lower molar percentage of cholesterol in hepatic bile, 3.4 +/- 0.4 vs. 2.9 +/- 0.2 mol %. This is probably due to an increased rate of conversion of cholesterol to bile acids in the hepatocyte. It is concluded that, in man, the liver may adapt well to changes in the enterohepatic circulation of bile acids, thereby maintaining output rates of biliary lipids at a relatively constant level.     

Serum bile acids as related to bile acid secretion in liver disease

The level of serum bile acids and their rate of secretion into the duodenum were measured in normal subjects and patients with cholesterol gallstones and hepatobiliary disease. These studies were undertaken to determine if changes in serum bile acids reflected alterations in bile acid secretion within the enterohepatic circulation, especially in association with disordered bile acid metabolism and liver dysfunction. To quantitate bile acid secretion, an intestinal marker-perfusion technique was used which measured duodenal output under stimulated but steady-state conditions. During these perfusion studies, serum bile acids were determined at hourly intervals. In normal subjects, serum bile acids during fasting were low (6.6±0.7 μM) with only a modest rise occurring after a fat meal (7.6±0.7 μM). The average bile acid secretion rate in these subjects was 1321 μmol/hr, and little fluctuation was noted in the serum levels (7.5±0.8 μM) during the perfusion studies. Patients with cholesterol galistones demonstrated a decreased rate of bile acid secretion at 714 μmol/hr but had normal serum values. After cholecystectomy, their bile acid secretion rate increased without any corresponding change in serum levels. In patients with liver disease, however, serum bile acids were elevated while bile acid secretion was reduced. Thus, in normal subjects the liver is quite capable of handling an increased endogenous bile acid return with only a small rise in serum levels. In liver disease, bile acid secretion is reduced while serum concentrations are increased, implying a defect in bile acid handling by the liver. In cholesterol gallstone disease, serum levels do not reflect the abnormality in bile acid metabolism. The relation between bile acid concentration in the serum and secretion rate into the enterohepatic circulation is therefore complex, depending on whether or not hepatic dysfunction is present or if bile acid metabolism is abnormal.