Cecal Bile Acid Research Articles

Dietary fat and gut microbiota interactions determine diet-induced obesity in mice

ObjectiveGut microbiota may promote positive energy balance; however, germfree mice can be either resistant or susceptible to diet-induced obesity (DIO) depending on the type of dietary intervention. We here sought to identify the dietary constituents that determine the susceptibility to body fat accretion in germfree (GF) mice. MethodsGF and specific pathogen free (SPF) male C57BL/6N mice were fed high-fat diets either based on lard or palm oil for 4 wks. Mice were metabolically characterized at the end of the feeding trial. FT-ICR-MS and UPLC-TOF-MS were used for cecal as well as hepatic metabolite profiling and cecal bile acids quantification, respectively. Hepatic gene expression was examined by qRT-PCR and cecal gut microbiota of SPF mice was analyzed by high-throughput 16S rRNA gene sequencing. ResultsGF mice, but not SPF mice, were completely DIO resistant when fed a cholesterol-rich lard-based high-fat diet, whereas on a cholesterol-free palm oil-based high-fat diet, DIO was independent of gut microbiota. In GF lard-fed mice, DIO resistance was conveyed by increased energy expenditure, preferential carbohydrate oxidation, and increased fecal fat and energy excretion. Cecal metabolite profiling revealed a shift in bile acid and steroid metabolites in these lean mice, with a significant rise in 17β-estradiol, which is known to stimulate energy expenditure and interfere with bile acid metabolism. Decreased cecal bile acid levels were associated with decreased hepatic expression of genes involved in bile acid synthesis. These metabolic adaptations were largely attenuated in GF mice fed the palm-oil based high-fat diet. We propose that an interaction of gut microbiota and cholesterol metabolism is essential for fat accretion in normal SPF mice fed cholesterol-rich lard as the main dietary fat source. This is supported by a positive correlation between bile acid levels and specific bacteria of the order Clostridiales (phylum Firmicutes) as a characteristic feature of normal SPF mice fed lard. ConclusionsIn conclusion, our study identified dietary cholesterol as a candidate ingredient affecting the crosstalk between gut microbiota and host metabolism.

Molecular Properties of Guar Gum and Pectin Modify Cecal Bile Acids, Microbiota, and Plasma Lipopolysaccharide-Binding Protein in Rats.

Bile acids (BAs) act as signaling molecules in various physiological processes, and are related to colonic microbiota composition as well as to different types of dietary fat and fiber. This study investigated whether guar gum and pectin—two fibers with distinct functional characteristics—affect BA profiles, microbiota composition, and gut metabolites in rats. Low- (LM) or high-methoxylated (HM) pectin, and low-, medium-, or high-molecular-weight (MW) guar gum were administered to rats that were fed either low- or high-fat diets. Cecal BAs, short-chain fatty acids (SCFA) and microbiota composition, and plasma lipopolysaccharide-binding protein (LBP) levels were analyzed, by using novel methodologies based on gas chromatography (BAs and SCFAs) and 16S rRNA gene sequencing on the Illumina MiSeq platform. Strong correlations were observed between cecal BA and SCFA levels, microbiota composition, and portal plasma LBP levels in rats on a high-fat diet. Notably, guar gum consumption with medium-MW increased the cecal amounts of cholic-, chenodeoxycholic-, and ursodeoxycholic acids as well as α-, β-, and ω-muricholic acids to a greater extent than other types of guar gum or the fiber-free control diet. In contrast, the amounts of cecal deoxycholic- and hyodeoxycholic acid were reduced with all types of guar gum independent of chain length. Differences in BA composition between pectin groups were less obvious, but cecal levels of α- and ω-muricholic acids were higher in rats fed LM as compared to HM pectin or the control diet. The inflammatory marker LBP was downregulated in rats fed medium-MW guar gum and HM pectin; these two fibers decreased the cecal abundance of Oscillospira and an unclassified genus in Ruminococcaceae, and increased that of an unclassified family in RF32. These results indicate that the molecular properties of guar gum and pectin are important for their ability to modulate cecal BA formation, gut microbiota composition, and high-fat diet induced inflammation.

High-fat Diet-induced Intestinal Hyperpermeability is Associated with Increased Bile Acids in the Large Intestine of Mice.

Metabolic syndrome is characterized by low-grade chronic systemic inflammation, which is associated with intestinal hyperpermeability. This study examined the effects of 3 high-fat diets (HFDs) composed of different fat sources (soybean oil and lard) on the intestinal permeability, tight junction (TJ) protein expression, and cecal bile acid (BA) concentrations in mice, and then analyzed their interrelations. C57/BL6 mice were fed the control diet, HFD (soybean oil), HFD (lard), and HFD (mix; containing equal concentrations of soybean oil and lard) for 8 wk. Glucose tolerance, intestinal permeability, TJ protein expression, and cecal BA concentration were evaluated. Feeding with the 3 HDFs similarly increased body weight, liver weight, and fat pad weight, and induced glucose intolerance and intestinal hyperpermeability. The expression of TJ proteins, zonula occludens-2 and junctional adhesion molecule-A, were lower in the colons of the 3 HFD groups than in the control group (P < 0.05), and these changes appeared to be related to intestinal hyperpermeability. Feeding with HFDs increased total secondary BA (SBA) and total BA concentrations along with increases in some individual BAs in the cecum. Significant positive correlations between intestinal permeability and the concentrations of most SBAs, such as deoxycholic acid and ω-muricholic acids, were detected (P < 0.05). These results suggest that the HFD-induced intestinal hyperpermeability is associated with increased BA secretion. The abundance of SBAs in the large intestine may be responsible for the hyperpermeability.

Inulin-Type Fructans with Different Degrees of Polymerization Improve Lipid Metabolism but Not Glucose Metabolism in Rats Fed a High-Fat Diet Under Energy Restriction

Inulin-type fructan ameliorates metabolic diseases associated with obesity in animals. However, relatively little information is available on the comparative effects of inulins with different degree of polymerization (DP) on the lipid or glucose metabolism. The objective of this study was to investigate the effect of inulins with various DP on metabolic disorders associated with obesity in rats fed a high-fat diet under food restriction. Rats were fed a high-fat diet supplemented with 5 % inulin-GR (Raftiline GR), inulin-Tokachi (Tokachi), or inulin-HP (Raftiline HP) without cellulose for 28 days at normal energy intakes or 14.5 % energy restriction. Under food restriction, the dietary inulin-Tokachi (mean DP 15) and -HP (mean DP 24), but not -GR (mean DP 10), reduced (p < 0.05) the serum cholesterol and triglyceride levels, and liver triglyceride concentration in rats, compared to the control diet. The cecal neutral steroid, bile acid, and propionate concentrations in the Tokachi and HP groups were higher (p < 0.05) than in the CONT group, and the cecal Bifidobacterium count in the Tokachi group was higher (p < 0.05) than in the other groups. Findings suggest that, depending on DP, dietary supplementation with inulin (DP 15 or DP 24) in rats fed a high-fat diet, regardless of food intake, positively modulates lipid metabolism and fecal microbiota but not glucose metabolism.

Human cecal bile acids: concentration and spectrum

To obtain information on the concentration and spectrum of bile acids in human cecal content, samples were obtained from 19 persons who had died an unnatural death from causes such as trauma, homicide, suicide, or drug overdose. Bile acid concentration was measured via an enzymatic assay for 3alpha-hydroxy bile acids; bile acid classes were determined by electrospray ionization mass spectrometry and individual bile acids by gas chromatography mass spectrometry and liquid chromatography mass spectrometry. The 3alpha-hydroxy bile acid concentration (mumol bile acid/ml cecal content) was 0.4 +/- 0.2 mM (mean +/- SD); the total 3-hydroxy bile acid concentration was 0.6 +/- 0.3 mM. The aqueous concentration of bile acids (supernatant after centrifugation) was identical, indicating that most bile acids were in solution. By liquid chromatography mass spectrometry, bile acids were mostly in unconjugated form (90 +/- 9%, mean +/- SD); sulfated, nonamidated bile acids were 7 +/- 5%, and nonsulfated amidated bile acids (glycine or taurine conjugates) were 3 +/- 7%. By gas chromatography mass spectrometry, 10 bile acids were identified: deoxycholic (34 +/- 16%), lithocholic (26 +/- 10%), and ursodeoxycholic (6 +/- 9), as well as their primary bile acid precursors cholic (6 +/- 9%) and chenodeoxycholic acid (7 +/- 8%). In addition, 3beta-hydroxy derivatives of some or all of these bile acids were present and averaged 27 +/- 18% of total bile acids, indicating that 3beta-hydroxy bile acids are normal constituents of cecal content. In the human cecum, deconjugation and dehydroxylation of bile acids are nearly complete, resulting in most bile acids being in unconjugated form at submicellar and subsecretory concentrations.

Retrograded Tapioca Starch Prevents Ovarian Hormone Deficiency-Induced Hypercholesterolemia

The purpose of this study was to examine whether retrograded tapioca starch (RS3-tapioca) prevents ovarian hormone deficiency-induced hypercholesterolemia. Six-month-old Wistar female rats were subjected to sham-operation or ovariectomy, and fed a cholesterol-free purified diet with or without RS3-tapioca (150 g/kg diet) instead of digestible cornstarch for 28 d. Body weight gain and food intake increased in ovariectomized rats (OVX-rats). Plasma total cholesterol concentration was lowered by RS3-tapioca in OVX rats, but not in sham-operated rats. Liver lipids increased in OVX-rats, but liver cholesterol concentration was not affected by ovariectomy and RS3-tapioca. CYP7A1 activity, small intestinal and cecal bile acid content, and fecal bile acid excretion were increased by RS3-tapioca. The ratio of cholic acid groups to chenodeoxycholic acid groups in the bile acid of the small intestine was increased by RS3-tapioca. Thus, the preventive effect of RS3-tapioca on the ovarian hormone deficiency-associated increase in plasma cholesterol concentration appears to be mediated by accelerated fecal excretion of bile acid and an increase in the intestinal pool of bile acid.

Composition of cecal bile acids in ex‐germfree mice inoculated with human intestinal bacteria

Germfree (GF) mice were orally inoculated with human fecal suspension or various components of human fecal microbiota. Three weeks after the inoculation, cecal bile acid composition of these mice was examined. More than 80% of total bile acids was deconjugated in the cecal contents of ex-GF mice associated with human fecal dilutions of 10(-2) or 10(-6), or anaerobic growth from a dilution of 10(-6). In these ex-GF mice, deoxycholic acid accounted for about 20% of total bile acids. In the cecal contents of ex-GF mice associated only with clostridia, unconjugated bile acids made up less than 40% of total bile acids, about half of those in other ex-GF groups. However, the percentage of deoxycholic acid in these mice was the same as that in the other groups. These results indicate that dominant anaerobic bacterial combination is efficient for deconjugation of primary bile acids, and that clostridia in the human feces may play an important role in 7alpha-dehydroxylation of unconjugated primary bile acids in the intestine.

Cholesterol-lowering effects of guar gum: changes in bile acid pools and intestinal reabsorption.

Soluble fibers such as guar gum (GG) may exert cholesterol-lowering effects. It is generally accepted that bile acid (BA) reabsorption in portal blood is reduced, thus limiting the capacity of BA to down-regulate liver cholesterol 7alpha-hydroxylase, the rate-limiting enzyme of BA synthesis. In the present work, rats were adapted to fiber-free (FF) or 5% GG diets (supplemented or not with 0.25% cholesterol), to investigate various aspects of enterohepatic BA cycling. GG in the diet at a level of 5% elicited a significant lowering of plasma cholesterol during the absorptive period, in cholesterol-free (-13%) or 0.25% cholesterol (-20%) diet conditions. In rats adapted to the GG diets, the small intestinal and cecal BA pools and the ileal vein-artery difference for BA were markedly enhanced; reabsorption in the cecal vein was also enhanced in these rats. [14C]Taurocholate absorption, determined in perfused ileal segments, was not significantly different in rats adapted to the FF or GG diet, suggesting that a greater flux of BA in the ileum might support a greater ileal BA reabsorption in rats adapted to the GG diet. In contrast, capacities for [14C]cholate absorption from the cecum at pH 6.5 were higher in rats adapted to the GG diet than to the FF diet. Acidification of the bulk medium in isolated cecum (from pH 7.1 down to pH 6.5 or 5.8) or addition of 100 mM volatile fatty acids was also found to stimulate cecal [14C]cholate absorption. These factors could contribute to accelerated cecal BA absorption in rats fed the GG diet. The effects of GG on steroid fecal excretion thus appear to accompany a greater intestinal BA absorption and portal flux to the liver. These results suggest that some mechanisms invoked to explain cholesterol-lowering effect of fibers should be reconsidered.

Absence of cecal secondary bile acids in gnotobiotic mice associated with two human intestinal bacteria with the ability to dehydroxylate bile acids in vitro.

Germ-free mice were orally inoculated with human intestinal 7alpha-dehydroxylating bacterial strains to evaluate their ability to transform bile acids in vivo. Three weeks after inoculation of the bacteria, cecal bile acids were examined. Among free-form bile acids, only beta-muricholic acid was detected in the cecal contents of gnotobiotic mice associated with Bacteroides distasonis strain K-5. No secondary bile acid was observed in the cecal contents of any of the gnotobiotic mice associated with 7alpha-dehydroxylating bacteria, Clostridium species strain TO-931 or Eubacterium species strain 36S.

White and Wholemeal Flours from Wheats of Low and Higher Apparent Metabolizable Energy Differ in Their Nutritional Effects in Rats ,

Wheats used for feeding poultry differ considerably in the ratio of soluble to insoluble non-starch polysaccharides (NSP) and apparent metabolizable energy (AME). We have examined effects of whole and white flour from a wheat of low (12.02 MJ/kg of dry matter) and high (14.52 MJ/kg of dry matter) AME in rats fed a cholesterol-free diet. NSP concentrations were higher in whole flour from the low AME wheat but similar in both white flours. In contrast to chickens, food intake and body weight gain of rats were unaffected by diet. Plasma cholesterol concentrations were lower in rats fed whole wheat and low AME wheat. Cecal bile acids and neutral sterol pools were larger in rats fed whole wheat but were unaffected by wheat type. Negative correlations were found between digesta steroid pools and plasma cholesterol, consistent with greater fecal steroid excretion. Cecal digesta was greater in rats fed whole wheat and low AME wheat. Digesta pH was lower in rats fed whole wheat, but there was a significant interaction between wheat and flour type with lower pH in rats fed low AME white flour. Total volatile fatty acids (VFA) and acetate and butyrate pools were larger in rats fed whole wheat than in those fed white flour. Total and individual VFA pools were larger in rats fed low AME flours than in those fed high AME flours, apparently due to greater cecal starch fermentation in the former. Factors affecting wheat AME in chickens affect important metabolic variables in rats and may have similar actions in other species including humans.

The cholesterol-lowering effect of guar gum is not the result of a simple diversion of bile acids toward fecal excretion.

The effects of partially hydrolyzed, nonviscous, guar gum (PHGG) on cholesterol metabolism and digestive balance have been compared with those of native guar gum (GUAR) in rats adapted to 0.4% cholesterol diets. Both types of guar gum elicited acidic fermentations in the large intestine, but only GUAR effectively lowered plasma cholesterol (P < 0.001), chiefly in the triglyceride-rich lipoprotein fraction. The biliary bile acid excretion was significantly enhanced in rats fed GUAR (P < 0.05), as well as the intestinal and cecal bile acid pool (P < 0.001). In rats fed GUAR and to a lesser extent in those fed PHGG, the fecal excretion of bile acids and neutral sterol was higher than in controls (P < 0.01). The digestive balance (cholesterol intake-steroid excretion) was positive in control rats (+47 mumol/d), whereas it was negative in rats fed GUAR (-20 mumol/d), which could involve a higher rate of endogenous cholesterol synthesis. In rats fed PHGG, the steroid balance remained slightly positive. Liver 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity was very low (22 pmol/min/mg protein), owing to cholesterol supplementation, in control rats or in rats fed PHGG, whereas it was markedly higher (+463%) in rats fed GUAR. In conclusion, even if PHGG does alter some parameters of the enterohepatic cycle of cholesterol and bile acids, its effects are not sufficient to elicit a significant cholesterol-lowering effect. The intestinal (ileal or cecal) reabsorption of bile acids was not reduced, but rather increased, by GUAR; nevertheless the intestinal capacities of reabsorption were overwhelmed by the enlargement of the digestive pool of bile acids. In the present model, induction of HMG-CoA reductase probably takes place in the presence of elevated portal bile acid concentrations.

Effect of cyclodextrin on plasma lipids and cholesterol metabolism in the rat

beta-Cyclodextrin (beta-CD) is a bile acid and sterol sequestrant produced by enzymatic modification of starch; this product has the potential to decrease plasma cholesterol. In contrast to the sequestrants having resin- or saponin-like properties, beta-CD is rapidly broken down by the large intestine microflora. beta-CD effects on cecal fermentations and lipid metabolism were thus investigated in rats adapted to semipurified diets containing 0%, 2.5%, or 5% beta-CD. In rats fed beta-CD diets, there was an enlargement of the cecum together with a dramatic increase in the cecal concentration of propionic acid (even with the 2.5% level, in moderately acidic pH conditions). Propionic acid produced in the cecum was readily absorbed and entirely taken up by the liver, whereas there was no significant acetic acid uptake. Dietary beta-CD was highly effective in enhancing bile acid entry into to the cecum: the cecal bile acids pool was 2.2 and 3.6-fold enlarged in rats fed the 2.5% and 5% beta-CD diets, respectively. The solubility percentage of bile acids decreased to approximately 25% in rats fed the beta-CD diets (v 51% in controls); the cecal concentration of soluble bile acids was thus relatively low in these animals. The fecal excretion of steroids was strongly enhanced by beta-CD, and bile acids excretion was practically proportional to the dietary beta-CD level. There was a net lipid-lowering effect of beta-CD, even at the 2.5% level. The effect was more pronounced on triglycerides than on cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of Bile Acid Pool Size, Turnover Time, and Distribution of Male Broiler Chicks During the First: 6 Weeks Posthatch Using SEHCAT, a Gamma Ray-Emitting Bile Acid Analogue ,

A bile acid analogue, SEHCAT (tauro-23-75 Se-selena-homocholic acid), was used to determine bile acid pool size, turnover time, and distribution in the developing broiler chick. Bile acid pool size was significantly affected by age and followed a quintic trend (a fifth degree polynomial). It remained steady until 30 days of age when it decreased significantly and then rose significantly at 37 days of age. The bile acid pool half-life remained constant until 28 days of age when it increased significantly and then held steady until it increased again at 8 wk of age following a quartic trend.The distribution of bile acids was affected by age with the amount in the gizzard, duodenum, cloaca, liver, and gall bladder varying significantly with age. Jejunal, ileal, and cecal bile acids did not vary significantly with age. Liver bile acid levels followed a quintic trend, rising until 23 days of age and dropping sharply at 30 days of age and holding steady.