Bile Acid Metabolism In Humans Research Articles

An integrated analysis of bile acid metabolism in humans with severe obesity.

Bile acids (BA) are vital regulators of metabolism. BAs are AQ6 secreted in the small intestine, reabsorbed, and transported back to the liver, where they can modulate metabolic functions. There is a paucity of data regarding the portal BA composition in humans. This study aimed to address this knowledge gap by investigating portal BA composition and the relation with peripheral and fecal BA dynamics in conjunction with the gut microbiome. Thirty-three individuals from the BARIA cohort were included. Portal plasma, peripheral plasma, and feces were collected. BA and C4 levels were measured employing mass spectrometry. FGF19 was measured using ELISA. Gut microbiota composition was determined through metagenomics analysis on stool samples. Considerable diversity in the portal BA composition was observed. The majority (n = 26) of individuals had a 9-fold higher portal than peripheral BA concentration. In contrast, 8 individuals showed lower portal BA concentration compared with peripheral and had higher levels of unconjugated and secondary BA in this compartment, suggesting more distal origin. The altered portal BA profile was associated with altered gut microbiota composition. In particular, taxa within Bacteroides were reduced in abundance in the feces of these individuals. Characterization of the portal BA composition in relation to peripheral and fecal BA increased insight into the dynamics of BA metabolism in individuals with obesity. Peripheral BA composition was much more diverse due to microbial metabolism. About 24% of the portal samples was surprisingly low in total BA; the underlying mechanism requires further exploration.

Gut Microbial Structural Variations as Determinants of Human Bile Acid Metabolism

Gut Microbial Structural Variations as Determinants of Human Bile Acid Metabolism

Effects of Daily Strawberry Intake (4 weeks) on Plasma Bile Acid Composition in Humans: A Randomized, Placebo-Controlled, Crossover Trial

Abstract Objectives Bile acids (BA) are liver derived compounds that undergo host and microbial metabolism. BA metabolites have multiple physiological roles including maintaining intestinal immune homeostasis. Dietary components influence BA metabolism/excretion through several mechanisms. This study aimed to evaluate the effects of daily strawberry intake (4 weeks) on bile acid metabolism in humans. Methods Thirty overweight/obese adults (age: 53 ± 7 years, BMI: 31 ± 4 kg/m,2) were recruited for this randomized, double-blind, placebo-controlled, crossover trial. Participants were randomized to 1 of 2 study sequences in a 1:1 ratio with 4 weeks washout period between two treatments. Participants consumed a strawberry beverage containing 25 g freeze-dried strawberry powder (∼1.75 servings of fresh strawberries) or energy-matched control beverage in random order twice a day for 4 weeks. Fasting blood samples were collected at weeks 0, 4, 8, and 12. Plasma samples (500 μL) were extracted using solid-phase C18 cartridges. An ultra-high performance liquid chromatography tandem mass spectrometry method was developed to quantitate bile acids and their metabolites (sulfates, glucuronides) in plasma. The method was validated in terms of linearity, sensitivity, recovery, and matrix effect. The data were analyzed using a paired student t-test with statistical significance set at P < 0.05. Results Twenty-nine glucuronidated and sulfated BAs were identified in plasma samples. Concentrations of primary BAs were not affected between the study treatments, whereas a significant decrease (P < 0.05) was observed in total secondary BAs (52 compounds) after 4 weeks of strawberry intake (11.2 ± 1.1 µmol/L) compared to placebo (18.3 ± 3.2 µmol/L). Individual secondary BAs including lithocholic acid (LCA), sulfo-glycolithocholic acid, and C24 oxidized LCA were significantly decreased after 4-week strawberry intake compared to placebo (P < 0.05). Conclusions Our results indicate that regular strawberry intake could lower pro-inflammatory LCA and other secondary BAs, suggesting a potential role of strawberry in ameliorating colonic inflammation and promoting gut health. Funding Sources This work was funded by the California Strawberry Commission and various donor funds to the Center for Nutrition Research, IIT.

Glycyrrhizin and glycyrrhetinic acid inhibits alpha-naphthyl isothiocyanate-induced liver injury and bile acid cycle disruption.

Alpha-naphthyl isothiocyanate (ANIT) is a common hepatotoxicant experimentally used to reproduce the pathologies of drug-induced liver injury in humans, but the mechanism of its toxicity remains unclear. To determine the metabolic alterations following ANIT exposure, metabolomic analyses was performed by use of liquid chromatography-mass spectrometry. Partial least squares discriminant analysis (PLS-DA) of liver, serum, bile, ileum, and cecum of vehicle- and ANIT-treated mice revealed significant alterations of individual bile acids, including increased tauroursodeoxycholic acid, taurohydrodeoxycholic acid, taurochenodeoxycholic acid, and taurodeoxycholic acid, and decreased ω-, β- and tauro-α/β- murideoxycholic acid, cholic acid, and taurocholic acid in the ANIT-treated groups. In accordance with these changes, ANIT treatment altered the expression of mRNAs encoded by genes responsible for the metabolism and transport of bile acids and cholesterol. Pre-treatment of glycyrrhizin (GL) and glycyrrhetinic acid (GA) prevented ANIT-induced liver damage and reversed the alteration of bile acid metabolites and Cyp7a1, Npc1l1, Mttp, and Acat2 mRNAs encoding bile acid transport and metabolism proteins. These results suggested that GL/GA could prevent drug-induced liver injury and ensuing disruption of bile acid metabolism in humans.

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.

Fish Oil Increases Bile Acid Synthesis in Male Patients with Hypertriglyceridemia

Fibrates are drugs of choice in patients with hypertriglyceridemia (HTG), but may increase the risk for gallstones by decreasing bile acid synthesis. Fish oil might be a therapeutic alternative, but its effect on bile acid metabolism in humans is unknown. We compared the effects of triglyceride-lowering therapy by fish oil or bezafibrate on cholesterol synthesis and bile acid metabolism in HTG. Cholesterol synthesis, bile acid pool sizes, and synthesis rates were compared between 9 male HTG patients and 10 normolipidemic controls matched for age, sex, and BMI. Effects of bezafibrate or fish oil were studied only in HTG patients in a randomized crossover trial. Patients had 14-fold higher serum triglyceride concentrations and greater cholesterol synthesis, as indicated by a 107% higher ratio of serum lathosterol to cholesterol (P < 0.01) than controls. The groups did not differ in bile acid metabolism. Both bezafibrate and fish oil reduced serum TG concentration (-68 and -51% vs. baseline, respectively). Compared with baseline, bezafibrate therapy was associated with reduced cholesterol synthesis (-25%, P = 0.009) without changes in bile acid synthesis rate and pool size. In contrast, fish oil increased bile acid synthesis (+31% vs. baseline, P = 0.07 and +53% vs. bezafibrate, P = 0.02) and altered bile acid distribution, as reflected by an increased ratio of the cholic acid (CA) synthesis rate to the chenodeoxycholic acid (CDCA) synthesis rate (+35% vs baseline, P = 0.05 and + 32% vs bezafibrate, P = 0.07) without effects on bile acid pool size or cholesterol synthesis. In conclusion, cholesterol synthesis is greater in HTG patients than in controls, whereas bile acid synthesis does not differ. Bezafibrate and fish oil have similar triglyceride-lowering capacities, but distinct effects on cholesterol synthesis. Bile acid synthesis is increased by fish oil, but not by bezafibrate therapy.

Effects of long-term ingestion of difructose anhydride III (DFA III) on intestinal bacteria and bile acid metabolism in humans

Changes in the intestinal microbiota of 10 human subjects with long-term ingestion of 3 g/d difructose anhydride III (DFA III; 4 persons, 2 months; 3 persons, 6 months; and 3 persons, 12 months) were examined by denaturing gradient gel electrophoresis (DGGE). According to the answers to questionnaires, the subjects were divided into two groups (constipated and normal). The DGGE profile was different for every individual and each subject had unique profiles of intestinal microbiota. In the DGGE profiles of constipated subjects, the intensities of bands related to Bacteroides spp. increased. Moreover, the DFA III-assimilating bacteria, Ruminococcus sp. were isolated from subjects who ingested DFA III for 12 months. These strains showed 95% similarity of their 16S rDNA sequences with that of Ruminococcus obeum ATCC 29174(T) (X85101) and produced large amounts of acetic acid. DFA III ingestion for 2 months tended to increase total organic acids in feces, and tended to decrease fecal pH and the secondary bile acid (SBA) ratio in total bile acids. The SBA ratio in total bile acids corresponded to fecal pH. The production of SBA was decreased by low pH in vitro. These results indicated that DFA III ingestion in humans tended to lower intestinal pH, inhibited bile acid 7alpha-dehydroxylation activities and also tended to decrease the SBA ratios in total bile acids. Moreover, as another cause for the decrease in the SBA ratio in total bile acids, it was suggested that the number of bile acid 7alpha-dehydroxylating bacteria were decreased by DFA III ingestion.

Suppression of bile acid synthesis by thyroid hormone in primary human hepatocytes

It is known that thyroid hormones alter the bile acid metabolism in humans, however the effect on individual enzymes has been difficult to elucidate. This is mainly due to the lack of human liver cell lines producing bile acids. We used cultures of primary human hepatocytes to study the effects of triiodothyronine (T(3)) on bile acid synthesis. Primary hepatocytes were isolated from liver tissue obtained from three different patients undergoing liver resection due to underlying malignancy. The hepatocytes were cultured under serum-free conditions and treated from d 1 to d 5 with culture containing 0.1 - 1000 nmol/L of T(3). Bile acid formation and mRNA levels of key enzymes were analysed. The lowest concentration of T(3) decreased cholic acid (CA) formation to 43%-53% of controls and chenodeoxycholic acid (CDCA) to 52%-75% of controls on d 5. The highest dose further decreased CA formation to 16%-48% of controls while CDCA formation remained at 50%-117% of controls. Expression of mRNA levels of cholesterol 7alpha-hydroxylase (CYP7A1) and sterol 12alpha-hydroxylase (CYP8B1) dose-dependently decreased. Sterol 27-hydroxylase (CYP27A1) levels also decreased, but not to the same extent. T(3) dose-dependently decreased total bile acid formation in parallel with decreased expression of CYP7A1 and CYP8B1. CA formation is inhibited to a higher degree than CDCA, resulting in a marked decrease in the CA /CDCA ratio.

Effects of pravastatin and ursodeoxycholic acid on cholesterol and bile acid metabolism in patients with cholesterol gallstones.

To investigate the effects of pravastatin and ursodeoxycholic acid (UDCA) on cholesterol and bile acid metabolism in humans, 41 patients with cholesterol gallstone disease were allocated to four groups and treated with pravastatin (20 mg/day), UDCA (600 mg/day), both pravastatin and UDCA, or neither drug (control) for 1-2 weeks prior to elective cholecystectomy. Cholesterol 7 alpha-hydroxylase activity and serum levels of total 7 alpha-hydroxycholesterol were significantly increased by pravastatin and unaffected by UDCA. 3-Hydroxy-3-methylglutaryl coenzyme A reductase activity was markedly increased by pravastatin and decreased by UDCA. UDCA significantly decreased biliary cholesterol concentration and the cholesterol saturation index and prolonged the nucleation time; however, pravastatin alone had little effect on biliary lithogenicity. Serum total and low-density lipoprotein (LDL)-cholesterol levels were reduced most by the combined administration of pravastatin and UDCA. In conclusion, at a dose of 20 mg/day, pravastatin increased bile acid synthesis but did not decrease biliary lithogenicity. UDCA had no significant effect on bile acid synthesis, but markedly decreased biliary lithogenicity.

Effects of lovastatin on biliary lipid secretion and bile acid metabolism in humans.

Lovastatin, an inhibitor of HMG-CoA reductase, lowers cholesterol saturation of bile. To determine the mechanism of this effect and further define the role of cholesterol synthesis in regulation of biliary lipid metabolism, we studied ten human volunteers in a control period and again after 5-6 weeks on lovastatin, 40 mg b.i.d. Mean sterol production from acetate in mononuclear leukocytes fell from 1.18 to 0.84 pmol/min per 10(6) cells on lovastatin (P less than 0.02). Concomitantly there was reduction in mean biliary secretion of cholesterol from 143 to 96 mumol/h (P less than 0.02). On lovastatin, mean pool size of bile acids by the Lindstedt method fell from 3193 to 2917 mumol (one-sided P = 0.05) and mean pool size by the one-sample method fell from 5158 to 4091 mumol (P less than 0.002). Lovastatin had no effect on mean fractional turnover rate of either cholic acid (0.77 vs. 0.74 day-1) or chenodeoxycholic acid (0.51 vs. 0.54 day-1). Mean total bile acid synthesis was lower on lovastatin (1443 vs. 1240 mumol/day), but the difference did not quite achieve statistical significance. In humans, inhibition of cholesterol synthesis by lovastatin lowers biliary cholesterol saturation by reducing cholesterol secretion into bile. Bile acid pool size, and perhaps bile acid synthesis, are also reduced by this inhibition.

Identification of 3 alpha,4 beta,7 alpha-trihydroxy-5 beta-cholanoic acid in human bile: reflection of a new pathway in bile acid metabolism in humans.

The chemical synthesis, nuclear magnetic resonance, and mass spectrometric characteristics of the first C-4 hydroxylated bile acid analogues are described. The data definitively confirm, for the first time, the identity of 3 alpha,4 beta,7 alpha-trihydroxy-5 beta-cholanoic acid in human fetal gallbladder bile. In addition, 3 alpha,4 beta,7 alpha-12 alpha-tetrahydroxy-5 beta-cholanoic was identified in the feces from healthy newborn infants many days after birth, indicating a hepatic origin for C-4 hydroxylation of bile acids. To our knowledge bile acids hydroxylated at the C-4 position of the steroid nucleus have never been previously recognized in any mammalian species. The finding of this novel bile acid which accounts for 5-15% of the total biliary bile acids in early gestation indicates that C-4 hydroxylation is a unique and important metabolic pathway in early human development.

Effect of 7-Ketolithocholic Acid on Bile Acid Metabolism in Humans

The effect of 7-ketolithocholic acid on biliary bile acid composition, cholesterol saturation, and as an intermediate in the conversion of chenodeoxycholic acid to ursodeoxycholic acid was investigated in 5 subjects with gallstones. After 7-ketolithocholic acid (400 mg/day) was administered orally for 14 days, biliary bile acid composition changed: The proportion of cholic acid decreased (from 45% to 19%), deoxycholic acid decreased (from 15% to 10%), chenodeoxycholic acid increased markedly (from 36% to 59%), ursodeoxycholic acid increased (from 36% to 59%), ursodeoxycholic acid increased (from 2% to 7%), and lithocholic acid increased (from 2% to 5%), while only trace amounts of 7-ketolithocholic acid were detected. During this treatment, the biliary lithogenic index fell from 2.6 to 0.9 and was accompanied by a pronounced drop in biliary cholesterol concentration. After biliary bile acid levels became constant [24-14C]chenodeoxycholic acid was given intravenously as a pulse-label, and the resultant biliary ursodeoxycholic acid and lithocholic acid specific activity curves showed a precursor--product relationship with chenodeoxycholic acid. Similarly, when uniformly labeled 7-[24-14C]ketolithocholic acid was fed (400 mg/day, 1000 +/- 100 dpm/mg) the specific activities of biliary chenodeoxycholic acid and ursodeoxycholic acid became constant and approximated each other, but these were only 75% as high as the fed 7-ketolithocholic acid. These results indicate that 7-ketolithocholic acid is absorbed, and suppresses endogenous bile acid production and biliary cholesterol secretion. Both isotopic experiments infer that ursodeoxycholic acid and lithocholic acid are formed from chenodeoxycholic acid and not from 7-ketolithocholic acid. The reduction in biliary lithogenic index and in cholesterol concentration suggest that low doses of 7-ketolithocholic acid may be effective in dissolving gallstones.

Age dependent differences in human bile acid metabolism and 7 alpha-dehydroxylation.

It has been suggested that transformation of secondary bile acids into (co)carcinogenic compounds may have a role in the development of cancer of the large bowel. Because of age dependent differences of this disease we undertook a study of cholic and deoxycholic acid metabolism of eleven young adults (group A, 20-30 years old) and eleven elderly persons (group B, 55-75 years old) with a double isotope dilution method. Daily food intake was standardized individually and gut transit time measured with radioopaque pellets and labelled chromium chloride. The 7 alpha-dehydroxylation fractions (the ratio of deoxycholic acid input rate from the large bowel to cholic acid synthesis rate) were higher in group B (P less than 0.01) due to higher deoxycholic acid input rates (P less than 0.005), especially when individuals from both groups with rapid gut transit were compared. As contributory factor was recognized the higher fractional turnover rate of cholic acid in group B. Pool sizes and synthesis rates of cholic acid and gut transit times were similar. In group A, but not in B, gut transit times correlated with deoxycholic acid input rates (P less than 0.01). The differences in bile acid metabolism may be related to a more effective colonic absorption of deoxycholic acid in the elderly persons with a concomitant decrease of active ileal absorption of cholic acid in the elderly persons. Differences in diet or gut transit time between both groups do not seem to be the underlying mechanism.

The formation of bile acid sulfates: a new pathway of bile acid metabolism in humans.

Bile acids are normally conjugated at the C24 carboxyl group with the amino acids taurine and glycine prior to their excretion into the bile of man and most higher species. In previous studies on biliary metabolites of C'4-labeled lithocholic acid in humans,' the expected taurine and glycine conjugates were observed, but approximately half of the labeled material occurred as more polar metabolites. In this report, data are presented which identify these compounds as the 3a-sulfate esters of glycolithocholic and taurolithocholic acids. The formation of these sulfate esters delineates a new pathway of bile acid metabolism in man, and has important implications for the clinical significance of lithocholic acid, an endogenous steroid with extensive biological toxicity. Methods.-Lithocholic acid-24-C'4 (50 tc, New England Nuclear Corp.) was given orally to two patients with functioning gallbladders, 36 hours prior to cholecystectomy for cholelithiasis. At operation, bile was obtained from the gallbladder. Thin-layer chromatography was performed using Silica Gel H (E. Merck A. G., Darmstadt, Germany) and the following phase systems: Butanol 1 :2 butanol 50, acetic acid 5, water 5 (pH 1); Butanol 3: butanol 50, 0.01 M Tris buffer 9.25, propionic acid 0.75 (pH 3.0); Propionic acid:' propionic acid 15, isoamyl acetate 20, water 5, n-propanol 10; S154: trimethylpentane 25, ethyl acetate 25, acetic acid 0.25. Radioactive spots on chromatoplates were detected with a Vanguard glass plate scanner (Vanguard Instrument Co., LaGrange, Ill.). Sulfate esters of glycolithocholic and taurolithocholic acids were prepared using pyridine-sulfur trioxide5 and crystallized as the ammonium salts. Details of the synthesis and properties of the compounds will be described separately. Solvolysis was performed using a modification of the method of Burstein and Lieberman.6 The steroid sulfate was dissolved in ethanol, acidified to pH 1 or less with 2 N HCI, and diluted with 9 volumes of acetone. The solvolysis mixture was then incubated at room temperature for one to three days. Some esterification occurred, and the resulting ethyl esters were hydrolyzed by refluxing for two hours in 5 per cent methanolic KOH. Results.-In the previous study, labeled biliary metabolites of orally administered lithocholic acid-24-C14 were shown to include glycolithocholic acid, taurolithocholic acid, and two polar compounds, I and II.' In this study, essentially similar results were obtained in both patients; four corresponding labeled biliary metabolites were observed on thin-layer chromatography using the Butanol 1 system. When bile was chromatographed with the Butanol 3 system, the labeled metabolites separated into two areas, A and B (Fig. 1). The compounds in area A, with the same mobility as glycolithocholic and taurolithocholic acid standards, were eluted and rechromatographed with the Butanol 1 system. Two radioactive spots, with mobilities corresponding to glycolithocholic acid and taurolithocholic acid, were identified. The