Bile acids

The Yin and Yang of bile acid action on tight junctions in a model colonic epithelium

Gastrointestinal epithelial barrier loss due to tight junction (TJ) dysfunction and bile acid‐induced diarrhea are common in patients with inflammatory diseases. Although excess colonic bile acids are known to alter mucosal permeability, few studies have compared the effects of specific bile acids on TJ function. We report that the primary bile acid, chenodeoxycholic acid (CDCA), and its 7α‐dehydroxylated derivative, lithocholic acid (LCA) have opposite effects on epithelial integrity in human colonic T84 cells. CDCA decreased transepithelial barrier resistance (pore) and increased paracellular 10 kDa dextran permeability (leak), effects that were enhanced by proinflammatory cytokines (PiC [ng/mL]: TNFα[10] + IL‐1ß[10] + IFNγ[30]). CDCA reversed the cation selectivity of the monolayer and decreased intercellular adhesion. In contrast, LCA alone did not alter any of these parameters, but attenuated the effects of CDCA ± PiC on paracellular permeability. CDCA, but not PiC, decreased occludin and not claudin‐2 protein expression; CDCA also decreased occludin localization. LCA ± CDCA had no effects on occludin or claudin expression/localization. While PiC and CDCA increased IL‐8 production, LCA reduced both basal and PiC ± CDCA‐induced IL‐8 production. TNFα + IL1ß increased IFNγ, which was enhanced by CDCA and attenuated by LCA. CDCA±PiC increased production of reactive oxygen species (ROS) that was attenuated by LCA. Finally, scavenging ROS attenuated CDCA's leak, but not pore actions, and LCA enhanced this effect. Thus, in T84 cells, CDCA plays a role in the inflammatory response causing barrier dysfunction, while LCA restores barrier integrity. Understanding the interplay of LCA, CDCA, and PiC could lead to innovative therapeutic strategies for inflammatory and diarrheal diseases.

Changes in bile acids metabolism during rat hepatocarcinogenesis: causative or unrelated?

In the present paper, we have aimed at studying the variations in the metabolism of bile acids occurring during an hepatocarcinogenic process induced in male Wistar Rats by the biphasic protocol of Solt and Farber. Bile acids concentrations was measured in the liver. The most significant changes have been observed 5 weeks after the beginning of the treatment, it means one week after the selection treatment consisting in 2-acetylaminofluorene administration: the increase in cholic acid, and of its intestinal metabolite, deoxycholic acid, and of alpha- and beta- muricholic acids, are likely to be a consequence of an acute effect of 2-acetylaminofluorene. To test for the putative implication of liver bile acids modifications in the selection effect of 2-acetylaminofluorene, diethyl-nitrosamine-pretreated rats were fed a diet containing 1% lithocholic acid, a treatment that induces essentially the same qualitative changes in liver bile acids, as 2-acetylaminofluorene does: no selection effect of lithocholic acid could be demonstrated. These results suggest that changes in bile acid metabolism occurring early in hepatocarcinogenesis are more likely to be secondary than causative events. The same conclusion comes from the results obtained later on in the process, where there is only a high increase in liver cholic acid and deoxycholic acid concentrations.

Chronic diarrhea in diabetes mellitus: mechanisms and an approach to diagnosis and treatment

In this study, our aim was to develop a practical strategy to facilitate the management of patients with diabetes mellitus and chronic diarrhea in a tertiary referral practice. We reviewed the pertinent English-language literature of the past 30 years that described the pathophysiologic mechanisms and treatment of patients with diabetic diarrhea and retrospectively reviewed the medical records of all patients with diabetic diarrhea examined at the Mayo Clinic during 1990. Three typical case studies are described to illustrate the diverse mechanisms that lead to chronic diarrhea in patients with diabetes. No report in the literature has systematically evaluated all the putative mechanisms of chronic diarrhea in any group of patients with diabetes. In our tertiary referral practice, diabetic diarrhea was frequently due to celiac sprue, bacterial overgrowth in the small bowel, or fecal incontinence in conjunction with anorectal dysfunction; however, in almost 50% of the patients, these causes were excluded, and abnormal intestinal motility or secretion was postulated to be one of the likely causes of the diarrhea. These data suggest a practical algorithm based on three sequential assessments: first, tests of blood and stool specimens and flexible sigmoidoscopy to detect evidence of malabsorption or disease in the distal colon; second, small bowel aspirate and biopsy if the results of initial blood or stool tests are abnormal or anorectal function tests if those test results are normal; and, finally, measurement of gastrointestinal transit or therapeutic trials with opioids, clonidine hydrochloride, and, rarely, cholestyramine resin or octreotide acetate (or both methods). The mechanisms whereby abnormal neural function due to diabetes results in altered digestive, secretory, absorptive, or motor function necessitate further elucidation. The management of chronic diarrhea in patients in a tertiary referral practice, however, can be based on a practical algorithm to determine the cause and to adopt specific treatment to correct it.

Bile acids: antioxidants or enhancers of peroxidation depending on lipid concentration

Using three different assay systems, we have discovered a heretofore unrecognized antioxidant property of bile acids at physiological concentrations. Bile acids inhibit peroxidation of the polyunsaturated lipid, linoleic acid, and of the highly fluorescent protein phycoerythrin. In part, the antioxidant activity results from scavenging of peroxyl radicals by direct oxidation of the bile acids. The most abundant products of the reaction of cholate and chenodeoxycholate with peroxyl radicals were studied in detail and shown to be the keto derivatives formed by oxidation of the 7 alpha-hydroxyl groups. Paradoxically, at linoleate concentrations higher than 1-2 mM, glycocholate up to approximately 10-14 mM enhances lipid peroxidation and inhibits only at higher concentrations. These findings may prove important in understanding the etiology of certain disease states of the biliary tract and intestine where lipid peroxidation may be involved and in providing a rationale for the positive epidemiological correlation between high lipid intake and higher fecal bile acid output and colon cancer.

Biliary bile acid profiles of domestic fowl as determined by high performance liquid chromatography and fast atom bombardment mass spectrometry

1. The biliary bile acid profiles of domestic chickens (Gallus domesticus), turkeys (Meleagris gallopavo), and ducks (Anas platyrhynchos) were determined by high performance liquid chromatography (HPLC) and fast atom bombardment mass spectrometry (FAB-MS). 2. Chenodeoxycholyltaurine and cholyltaurine were the predominant bile acids in chicken and turkey bile, whereas duck bile contained primarily chenodeoxycholyltaurine and phocaecholyltaurine. 3. Allocholyltaurine was also detected in chicken and turkey bile, but not in duck bile. 4. FAB-MS analyses of individual HPLC peak fractions from chicken and duck bile extracts confirmed the presence of either taurine-conjugated dihydroxy- or trihydroxycholanoates. 5. Direct FAB-MS analyses of avian bile extracts not subjected to HPLC permitted a rapid assessment of the relative proportion of taurine-conjugated dihydroxy- to trihydroxycholanoates.

Bile acid synthesis by cultured rabbit hepatocytes: stimulation by three lipoprotein fractions

Bile acid and cholesterol synthesis were measured in monolayer cultures of rabbit hepatocytes maintained in a defined culture medium. In the absence of lipoproteins, bile acid synthesis and secretion were correlated with cholesterol synthesis and were increased 245% by mevalonolactone (10 mM) and inhibited 45% by lovastatin (50 micrograms/ml) over 24 h. When included in the culture medium, normal rabbit plasma low-density and high-density lipoproteins increased bile acid synthesis and secretion by up to 140% of values obtained without lipoproteins in hepatocytes from normal or cholestyramine-fed rabbits. Three cholesterol-rich lipoprotein fractions (beta-very low density, low density and high density) also were isolated from rabbits fed 1% cholesterol for 14 days. When added to rabbit hepatocyte cultures, each fraction markedly increased hepatocellular cholesterol content, stimulated bile acid synthesis and secretion in a dose-dependent manner, and inhibited cholesterol synthesis from radioactive acetate. These data indicate that three different lipoprotein fractions can provide cholesterol for uptake and subsequent breakdown to bile acids by cultured rabbit hepatocytes.

Bile acid synthesis and secretion by rabbit hepatocytes in primary monolayer culture: comparison with rat hepatocytes

Rabbit hepatocytes isolated after liver perfusion with collagenase were maintained in primary monolayer culture for periods up to 96 h. Bile acid synthesis and secretion was measured by capillary gas-liquid chromatography and by a rapid enzymatic-bioluminescence assay. As expected from the bile acid profile of rabbit gallbladder bile, cholic acid was the only bile acid synthesized in detectable amounts and was produced at a linear rate of 170 pmol/h per mg cell protein from 24 to 96 h in culture. Ketoconazole (20 microM) inhibited cholic acid synthesis and secretion by 78%, whereas the bile acids chenodeoxycholic acid (100 microM), deoxycholic acid (100 microM) or lithocholic acid (2 microM) had no effect. When rat hepatocytes were cultured under identical conditions, the rate of bile acid synthesis was found to be only 12 pmol/h per mg cell protein, a value in agreement with previous work. The large difference in rates of bile acid synthesis between rabbit and rat hepatocytes may be due to rapid loss of cytochrome P-450 from rat hepatocytes when placed in monolayer culture. Although reportedly active in cholesterol 7 alpha-hydroxylation, form 4 cytochrome P-450 levels in rabbit hepatocytes did not correlate with rates of bile acid synthesis.

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.