The effect of bile and bile salts on the uptake and cleavage of β-carotene into retinol ester (vitamin A ester) by intestinal slices

Associations between the Gut Microbiota, Urinary Metabolites, and Diet in Women during the Third Trimester of Pregnancy

Background

Pregnancy causes many metabolic and physiologic changes. However, associations between gut microbiota, dietary intake, and urinary metabolites are poorly characterized in pregnant women.

Objectives

The research objective was to identify dietary and microbial associations with urinary metabolites during pregnancy to elucidate potential biomarkers and microbial targets to improve maternal-fetal health. This is a secondary outcome of the study.

Methods

Pregnant women (n = 27) in the Pregnancy EAting and POstpartum Diapers pilot study provided dietary intake information in addition to fecal and urine samples at 36 wk gestation. The gut microbiota was characterized following fecal DNA extraction and 16S rRNA gene sequencing. Urinary metabolites were identified using liquid chromatography high-resolution mass spectrometry.

Results

Urinary glycocholate was consistently and negatively correlated with α-carotene intake. There were 9 significant correlations between microbial taxa and urinary metabolites and 13 significant correlations between microbial taxa and dietary intake. On average, Bacteroides were the most abundant taxon in the participants' gut microbiotas. Notably, the gut microbiotas of some pregnant women were not dominated by this taxon. Bacteroides-dominant women consumed more protein, fat, and sodium, and their gut microbiotas had lower alpha diversity than those of nondominant participants.

Conclusions

Several urinary metabolites and microbial taxa were associated with maternal diet and gastrointestinal community composition during the third trimester of pregnancy. Future work should determine the mechanisms underlying the associations identified herein.

Review on Bile Acids: Effects of the Gut Microbiome, Interactions with Dietary Fiber, and Alterations in the Bioaccessibility of Bioactive Compounds

Bile acids are cholesterol-derived steroid molecules that serve various metabolic functions, particularly in the digestion of lipids. Gut microbes produce unconjugated and secondary bile acids through deconjugation and dehydroxylation reactions, respectively. Alterations in the gut microbiota have profound effects on bile acid metabolism, which can result in the development of gastrointestinal and metabolic diseases. Emerging research shows that diets rich in dietary fiber have substantial effects on the microbiota and human health. Plant-based foods are primary sources of bioactive compounds and dietary fiber, which are metabolized by microbes to produce different metabolites. However, the bioaccessibility of these compounds are not well-defined. In this review, we discuss the interaction of bile acids with dietary fiber, the gut microbiota, and their role in the bioaccessibility of bioactive compounds. To understand the possible mechanism by which bile acids bind fiber, molecular docking was performed between different dietary fiber and bile salts.

Effect of Bile on Absorption of Mepitiostane by the Lymphatic System in Rats

The effects of bile and site of gastrointestinal absorption on the lymphatic absorption of the highly lipophilic drug, mepitiostane were examined using thoracic duct-cannulated rats. The lymphatic absorption from the small intestine was very small in the absence of bile compared with that when bile was present. The lymphatic absorption was greatest when drug was administered to the upper small intestine with bile, was smaller for the lower regions of the small intestine, and was negligible for the stomach and the large intestine. A correlation was observed between the extent of lymphatic absorption and the secretion of chylomicron and very low density lipoproteins after administration to various regions with or without bile. The portal absorption data of mepitiostane confirmed that site specificity occurs in the partition of drug between blood and lymph.

Influence of dietary spices on the in vivo absorption of ingested β-carotene in experimental rats

Animal studies were conducted to evaluate the influence of dietary spice compounds, piperine, capsaicin and ginger, on the absorption of orally administered β-carotene and its conversion to vitamin A. In rats maintained on these spice-containing diets for 8 weeks, concentrations of β-carotene and retinol were determined in the serum, liver and intestine 4 h after a single oral administration of β-carotene. β-Carotene concentration was significantly increased in the serum, liver and intestine of piperine- and ginger-fed rats, suggesting improved absorption of β-carotene. However, retinol concentration was not significantly changed in these animals, suggesting that the bioconversion of β-carotene to vitamin A was not similarly influenced. Between the two enzymes involved in the bioconversion of β-carotene to vitamin A, the activity of intestinal and hepatic β-carotene 15,15′-dioxygenase was either unaffected or lowered by these spice treatments. The activity of intestinal and hepatic retinal reductase was unaffected by the dietary spices. Activities of these two enzymes involved in the bioconversion of β-carotene to retinal were inhibited by the test spices in vitro, thus corroborating with the in vivo observation. Although the bioconversion of β-carotene was not promoted, increased absorption and tissue levels of β-carotene by the dietary spices may contribute to a higher antioxidant protection.

beta-Carotene deficiency in cholestatic liver disease of childhood is caused by beta-carotene malabsorption

BACKGROUND

: Depletion of beta-carotene (b-c) has not been extensively studied in children with chronic cholestatic liver disease.

PATIENTS AND METHODS

: We assessed b-c serum concentration in 53 children with cholestatic liver disease: 19 patients operated on for biliary atresia, 12 with Alagille syndrome, and 22 with progressive familial intrahepatic cholestasis. To test b-c absorption, 6 children with chronic cholestasis received a load of 10 mg b-c/kg body weight.

RESULTS

: We found decreased b-c concentrations in 45 patients. The absorption of b-c was not detectable in 5 of 6 children studied.

CONCLUSIONS

: b-c depletion is a common problem of chronic cholestatic liver disease in childhood that can be attributed to disturbed intestinal absorption.

{beta}-Apocarotenoids do not significantly activate retinoic acid receptors {alpha} or {beta}

beta-Carotene oxygenase 2 cleaves beta-carotene asymmetrically at non-central double bonds of the polyene chain, yielding apocarotenal molecules. The hypothesis tested was that apocarotenoids are able to stimulate transcription by activating retinoic acid receptors (RARs). The effects of long- and short-chain apocarotenals and apocarotenoic acids on the activation of RARalpha and RARbeta transfected into monkey kidney fibroblast cells (CV-1) were investigated. We synthesized or purified beta-apo-8'-carotenoic acid (apo-8'-CA), beta-apo-14'-carotenoic acid (apo-14'-CA), beta-cyclocitral (BCL), beta-cyclogernanic acid (BCA), beta-ionone (BI), beta-ionylideneacetaldehyde (BIA) beta-ionylideneacetic acid (BIAA) and a C13 ketone, beta-apo-13-carotenone (C13). None of the apocarotenoids tested showed significant transactivation activity for the RARs when compared with all-trans retinoic acid (RA). The results suggest that biological effects of these apocarotenoids are through mechanisms other than activation of RARalpha and beta.

Comparative in vitro and in vivo absorption of 2-hydroxy-4(methylthio) butanoic acid and methionine in the broiler chicken

Poultry diets are typically supplemented with DL-2-hydroxy-4(methylthio) butanoic acid (HMTBA, or the hydroxy analog of methionine) or DL-methionine (DLM). Although HMTBA and DLM provide methionine activity, they are structurally distinct molecules with different physiological characteristics until they are converted to L-methionine. The relative rates of intestinal HMTBA vs. DLM absorption have been controversial, and it has been claimed that HMTBA is not fully absorbed. We measured the uptake of HMTBA and DLM in an in vitro everted intestinal slice model. Sections of intestinal slices (jejunum and ileum) were incubated with 0.1 to 50 mM HMTBA that was radiolabeled or DLM that was radiolabeled, and absorption was measured by scintillation counting. The HMTBA uptake was equal to or greater than DLM absorption in each tissue and at every time point with one exception. Furthermore, the rates of HMTBA absorption were always equal to or significantly greater than DLM uptake. In a separate in vivo experiment, absorption of HMTBA and L-methionine was monitored along the entire gastrointestinal (GI) tract. Broilers were fed commercial-type corn-soy diets supplemented with 0.21% HMTBA. Digesta was collected from crop, proventriculus, gizzard, duodenum, jejunum, ileum, large intestine, and cloaca and analyzed for the concentration of free HMTBA and free methionine in each compartment. These studies demonstrated that HMTBA is absorbed completely and along the entire GI tract, especially the upper GI tract. Furthermore, there was a higher concentration of free L-methionine than HMTBA in the digesta from every segment distal to the gizzard.

Specificity of the retinol transporter of the rat small intestine brush border

The uptake of vitamin A (all-trans-retinol) by the absorptive cell of the small intestine is the necessary first step in its utilization by the organism and appears to involve a specific carrier that operates by facilitated diffusion. We investigated the specificity of that process by determining the absorption of all-trans-, 13-cis-, and 9-cis-retinol, 3-dehydroretinol, and retinal (vitamin A aldehyde) by gut sheets from the small intestine of suckling rats. We found that radiolabeled all-trans-retinol and 3-dehydroretinol were absorbed at similar rates and that approximately 60% of the total absorption could be competed for by unlabeled all-trans-retinol. A similar level of inhibition could be achieved for all-trans-retinol absorption by treating the intestinal sheets with N-ethylmaleimide. The noncompetable, noninhibitable component of all-trans-retinol absorption corresponded to the total absorption rate for 13-cis- and 9-cis-retinol and retinal. Additionally, we found that the relative rates of transport of these retinoids were unrelated to their relative affinities for the abundant absorptive cell retinoid carrier protein, cellular retinol-binding protein, type II, and were not driven by esterification. This confirms that the absorption of retinol is facilitated by a transporter and establishes that it is specific for the all-trans alcohol forms of vitamin A.

Methodology for the determination of bioavailability of labeled residues

Methods are described for the determination of bioavailability of lipo- and hydro- soluble compounds in the rat. These procedures involve catheterization of the portal vein and/or intestinal lymphatics to study absorption in unanesthetized animals. Catheterization of the common bile duct prevents recycling of materials through the entero-porto-hepato-biliary circulation (EPHBC). Steady-state conditions are ensured by constant infusion of bile or a solution of bile acids into the stomach or duodenum. The techniques and physiological considerations discussed in detail here have resulted in new proposed animal preparations, of value in the accurate determination of the bioavailability of labeled residues ingested by the second species. Since intake must be adequate to permit meaningful conclusions, the concentration of radioactivity in the harvested homogenized tissue is increased by lyophilization. The lyophilized material is compressed into pellets of adequate size. The animals, kept in restraining cages to prevent coprophagy, are allowed to eat the labeled residue spontaneously, if necessary, for 48 and even 72 hr. Bile, urine, and feces are collected for a sufficient length of time to allow quantitative excretion of the labeled residue, if no absorption takes place. Collection of these excreta must be complete. It is essential to account for most-if not all-of the radioactivity administered. Data so obtained allow an accurate balance between intake and excretion of the labeled residue. The presence of radioactivity in the intestinal wall, carcass, liver, and urine is indicative of absorption. The appearance of radioactivity in the bile also indicates absorption, in addition to suggesting that the compound(s) may undergo EPHBC. The extent of recovery of the administered radioactivity in the luminal contents and feces indicates the extent to which the labeled residue is not bioavailable. Evaluation of data obtained with these new animal models should permit corresponding upward adjustments of the minimum levels of residues allowable in the tissue of animals intended for human consumption.

The roles of bile salts in the uptake of beta-carotene and retinol by rat everted gut sacs

The effects of bile salts, Tween 20 and hexadecyltrimethylammonium-bromide on the uptake of beta-[3H]carotene and [3H]retinol by rat-everted gut sacs were studied in vitro under conditions simulating those present in the intestinal lumen during lipid absorption. 2. Micellar solutions significantly enhanced uptake over emulsions. Maximum uptake occurred at the critical micellar concentration of the bile salts mixture. At higher detergent concentrations beta-carotene uptake declined sharply; retinol absorption remained high. 3. In beta-carotene absorption bile salts functioned not only as micellar solubilizers but also may have been required for interaction with the cell membrane or as a transport carrier. In retinol uptake their primary function appeared only to be micellar solubilization. Both uptake and efflux of substrates were enhanced in bile salt micellar solutions compared to the other detergents. 4. Beta-carotene cleavage and conversion to retinyl esters occurred only in bile salts solutions. Retinol esterification was seen with all detergents. These effects increased as the tri/dihydroxy bile salts ratio was increased. 5. Beta-carotene uptake appeared to be reversible and passive at low concentrations. Retinol uptake was reversible, 7-30 times more rapid, and partially inhibited by 2,4-dinitrophenol at higher concentrations. An energy-requiring step may have been rate limiting.

BIOSYNTHESIS OF VITAMIN A WITH RAT INTESTINAL ENZYMES

Vitamin A is synthesized from beta-carotene in cell-free homogenates of rat intestinal mucosa, the biosynthetic enzymatic activity being present in the soluble protein fraction of the homogenate. Also required are a heat-stable factor in the particulate fraction, molecular oxygen, and bile salts. The reaction is stimulated by glutathione. The product, obtained in yields of up to 50 percent, has been identified as vitamin A aldehyde (retinal) by way of its semicarbazone derivative. The reaction mechanism involves the central cleavage of beta-carotene into two molecules of retinal.