Effect of bile salts on colonic mucus secretion in isolated vascularly perfused rat colon

Safety of surfactant excipients in oral drug formulations

Surfactants are a diverse group of compounds that share the capacity to adsorb at the boundary between distinct phases of matter. They are used as pharmaceutical excipients, food additives, emulsifiers in cosmetics, and as household/industrial detergents. This review outlines the interaction of surfactant-type excipients present in oral pharmaceutical dosage forms with the intestinal epithelium of the gastrointestinal (GI) tract. Many surfactants permitted for human consumption in oral products reduce intestinal epithelial cell viability in vitro and alter barrier integrity in epithelial cell monolayers, isolated GI tissue mucosae, and in animal models. This suggests a degree of mis-match for predicting safety issues in humans from such models. Recent controversial preclinical research also infers that some widely used emulsifiers used in oral products may be linked to ulcerative colitis, some metabolic disorders, and cancers. We review a wide range of surfactant excipients in oral dosage forms regarding their interactions with the GI tract. Safety data is reviewed across in vitro, ex vivo, pre-clinical animal, and human studies. The factors that may mitigate against some of the potentially abrasive effects of surfactants on GI epithelia observed in pre-clinical studies are summarised. We conclude with a perspective on the overall safety of surfactants in oral pharmaceutical dosage forms, which has relevance for delivery system development.

Diet, microbiota, and the mucus layer: The guardians of our health

The intestinal tract is an ecosystem in which the resident microbiota lives in symbiosis with its host. This symbiotic relationship is key to maintaining overall health, with dietary habits of the host representing one of the main external factors shaping the microbiome-host relationship. Diets high in fiber and low in fat and sugars, as opposed to Western and high-fat diets, have been shown to have a beneficial effect on intestinal health by promoting the growth of beneficial bacteria, improve mucus barrier function and immune tolerance, while inhibiting pro-inflammatory responses and their downstream effects. On the contrary, diets low in fiber and high in fat and sugars have been associated with alterations in microbiota composition/functionality and the subsequent development of chronic diseases such as food allergies, inflammatory bowel disease, and metabolic disease. In this review, we provided an updated overview of the current understanding of the connection between diet, microbiota, and health, with a special focus on the role of Western and high-fat diets in shaping intestinal homeostasis by modulating the gut microbiota.

Impact of Bile Acid Diarrhea in Patients With Diarrhea-Predominant Irritable Bowel Syndrome on Symptoms and Quality of Life

BACKGROUND & AIMS

Bile acid diarrhea (BAD) affects approximately a quarter of patients with irritable bowel syndrome with diarrhea (IBS-D). We aimed to compare the demographics, bowel and somatic symptoms, and quality of life of patients with IBS-D, with or without BAD.

METHODS

On one occasion, patients with IBS-D (positive for Rome III criteria) completed the following questionnaires: bowel disease questionnaire, Hospital Anxiety and Depression inventory, general quality of life (Symptom Checklist-90), and IBS-specific quality of life. A fasting serum C4 level higher than 52.5 ng/mL was used as a biomarker for BAD. Statistical analysis included a multiple variable logistic model to identify strong predictors of BAD in IBS-D.

RESULTS

Among 219 patients (79% female) with IBS-D, 44 had BAD; the BAD group was significantly older and had a higher body mass index than the patients without BAD. Patients with BAD had more severe bowel dysfunction and impact on IBS-specific quality of life (need of toilet proximity) compared with patients with IBS-D without BAD. Patients with BAD were more likely than other IBS-D groups to receive antidiarrheals, bile acid binders, and antacid secretory agents. The severity of diarrhea and need of toilet proximity were predictors of BAD in IBS-D (P < .01). Patients with BAD were more likely to have a depression score higher than 8 on the Hospital Anxiety and Depression inventory.

CONCLUSIONS

There is a greater impact on bowel and somatic symptoms and quality of life in IBS-D with BAD compared with IBS-D without BAD. Screening for BAD in IBS-D is especially relevant, with more severe and frequent diarrhea along with urgency.

Inhibition of CFTR-mediated intestinal chloride secretion as potential therapy for bile acid diarrhea

Bile acid diarrhea (BAD) is common with ileal resection, Crohn's disease, and diarrhea-predominant irritable bowel syndrome. Here, we demonstrate the efficacy of cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor (R)-benzopyrimido-pyrrolo-oxazine-dione-27 (BPO-27) in reducing bile acid-induced fluid and electrolyte secretion in colon. Short-circuit current measurements in human T84 colonic epithelial cells and planar colonic enteroid cultures showed a robust secretory response following mucosal but not serosal addition of chenodeoxycholic acid (CDCA) or its taurine conjugate, which was fully blocked by CFTR inhibitors, including (R)-BPO-27. (R)-BPO-27 also fully blocked CDCA-induced secretory current in murine colon. CFTR activation by CDCA primarily involved Ca2+ signaling. In closed colonic loops in vivo, luminal CDCA produced a robust secretory response, which was reduced by ∼70% by (R)-BPO-27 or in CFTR-deficient mice. In a rat model of BAD produced by intracolonic infusion of CDCA, (R)-BPO-27 reduced the elevation in stool water content by >55%. These results implicate CFTR activation in the colon as a major prosecretory mechanism of CDCA, a bile acid implicated in BAD, and support the potential therapeutic efficacy of CFTR inhibition in bile acid-associated diarrheas.-Duan, T., Cil, O., Tse, C. M., Sarker, R., Lin, R., Donowitz, M., Verkman, A. S. Inhibition of CFTR-mediated intestinal chloride secretion as potential therapy for bile acid diarrhea.

A fiber-deprived diet disturbs the fine-scale spatial architecture of the murine colon microbiome

Compartmentalization of the gut microbiota is thought to be important to system function, but the extent of spatial organization in the gut ecosystem remains poorly understood. Here, we profile the murine colonic microbiota along longitudinal and lateral axes using laser capture microdissection. We found fine-scale spatial structuring of the microbiota marked by gradients in composition and diversity along the length of the colon. Privation of fiber reduces the diversity of the microbiota and disrupts longitudinal and lateral gradients in microbiota composition. Both mucus-adjacent and luminal communities are influenced by the absence of dietary fiber, with the loss of a characteristic distal colon microbiota and a reduction in the mucosa-adjacent community, concomitant with depletion of the mucus layer. These results indicate that diet has not only global but also local effects on the composition of the gut microbiota, which may affect function and resilience differently depending on location.

Leaky gut: mechanisms, measurement and clinical implications in humans

The objectives of this review on 'leaky gut' for clinicians are to discuss the components of the intestinal barrier, the diverse measurements of intestinal permeability, their perturbation in non-inflammatory 'stressed states' and the impact of treatment with dietary factors. Information on 'healthy' or 'leaky' gut in the public domain requires confirmation before endorsing dietary exclusions, replacement with non-irritating foods (such as fermented foods) or use of supplements to repair the damage. The intestinal barrier includes surface mucus, epithelial layer and immune defences. Epithelial permeability results from increased paracellular transport, apoptosis or transcellular permeability. Barrier function can be tested in vivo using orally administered probe molecules or in vitro using mucosal biopsies from humans, exposing the colonic mucosa from rats or mice or cell layers to extracts of colonic mucosa or stool from human patients. Assessment of intestinal barrier requires measurements beyond the epithelial layer. 'Stress' disorders such as endurance exercise, non-steroidal anti-inflammatory drugs administration, pregnancy and surfactants (such as bile acids and dietary factors such as emulsifiers) increase permeability. Dietary factors can reverse intestinal leakiness and mucosal damage in the 'stress' disorders. Whereas inflammatory or ulcerating intestinal diseases result in leaky gut, no such disease can be cured by simply normalising intestinal barrier function. It is still unproven that restoring barrier function can ameliorate clinical manifestations in GI or systemic diseases. Clinicians should be aware of the potential of barrier dysfunction in GI diseases and of the barrier as a target for future therapy.

Guts and Gall: Bile Acids in Regulation of Intestinal Epithelial Function in Health and Disease

Epithelial cells line the entire surface of the gastrointestinal tract and its accessory organs where they primarily function in transporting digestive enzymes, nutrients, electrolytes, and fluid to and from the luminal contents. At the same time, epithelial cells are responsible for forming a physical and biochemical barrier that prevents the entry into the body of harmful agents, such as bacteria and their toxins. Dysregulation of epithelial transport and barrier function is associated with the pathogenesis of a number of conditions throughout the intestine, such as inflammatory bowel disease, chronic diarrhea, pancreatitis, reflux esophagitis, and cancer. Driven by discovery of specific receptors on intestinal epithelial cells, new insights into mechanisms that control their synthesis and enterohepatic circulation, and a growing appreciation of their roles as bioactive bacterial metabolites, bile acids are currently receiving a great deal of interest as critical regulators of epithelial function in health and disease. This review aims to summarize recent advances in this field and to highlight how bile acids are now emerging as exciting new targets for disease intervention.

Chronic diarrhoea following surgery for colon cancer-frequency, causes and treatment options

PURPOSE

The growing population of survivors after colon cancer warrants increased attention to the long-term outcome of surgical treatment. The change in bowel anatomy after resection disrupts normal gastrointestinal function and may cause symptoms. Thus, many patients surviving colon cancer have to cope with bowel dysfunction for the rest of their lives. We here aim to provide an overview of the literature on this topic.

METHODS

We review long-term functional outcomes of surgical treatment for colon cancer, the underlying pathology, and treatment options.

RESULTS

Common symptoms include constipation, urge for defecation and diarrhoea. Causes of diarrhoea after colon cancer surgery are sparsely studied, but they probably include bile acid malabsorption, small intestinal bacterial overgrowth and disruption of the ileal brake. Specific diagnosis should be made to allow individual treatment based on the underlying pathology. Studies on treatment of functional problems after surgery for colon cancer are extremely few, but some lessons can be drawn from the treatment of other patient groups having undergone colon surgery.

CONCLUSION

Diarrhoea is likely a common long-term complication after colon cancer surgery. Attention to this complication and a specific diagnosis will aid the targeted treatment of patients suffering from this complication.

The bile acids, deoxycholic acid and ursodeoxycholic acid, regulate colonic epithelial wound healing

The intestinal epithelium constitutes an innate barrier which, upon injury, undergoes self-repair processes known as restitution. Although bile acids are known as important regulators of epithelial function in health and disease, their effects on wound healing processes are not yet clear. Here we set out to investigate the effects of the colonic bile acids, deoxycholic acid (DCA) and ursodeoxycholic acid (UDCA), on epithelial restitution. Wound healing in T₈₄ cell monolayers grown on transparent, permeable supports was assessed over 48 h with or without bile acids. Cell migration was measured in Boyden chambers. mRNA and protein expression were measured by RT-PCR and Western blotting. DCA (50-150 µM) significantly inhibited wound closure in cultured epithelial monolayers and attenuated cell migration in Boyden chamber assays. DCA also induced nuclear accumulation of the farnesoid X receptor (FXR), whereas an FXR agonist, GW4064 (10 µM), inhibited wound closure. Both DCA and GW4064 attenuated the expression of CFTR Cl^- channels, whereas inhibition of CFTR activity with either CFTR-_inh-172 (10 µM) or GlyH-101 (25 µM) also prevented wound healing. Promoter/reporter assays revealed that FXR-induced downregulation of CFTR is mediated at the transcriptional level. In contrast, UDCA (50-150 µM) enhanced wound healing in vitro and prevented the effects of DCA. Finally, DCA inhibited and UDCA promoted mucosal healing in an in vivo mouse model. In conclusion, these studies suggest bile acids are important regulators of epithelial wound healing and are therefore good targets for development of new drugs to modulate intestinal barrier function in disease treatment. NEW & NOTEWORTHY The secondary bile acid, deoxycholic acid, inhibits colonic epithelial wound healing, an effect which appears to be mediated by activation of the nuclear bile acid receptor, FXR, with subsequent downregulation of CFTR expression and activity. In contrast, ursodeoxycholic acid promotes wound healing, suggesting it may provide an alternative approach to prevent the losses of barrier function that are associated with mucosal inflammation in IBD patients.

The Effect of Deoxycholic Acid on Secretion and Motility in the Rat and Guinea Pig Large Intestine

Background/Aims

Bile acid is an important luminal factor that affects gastrointestinal motility and secretion. We investigated the effect of bile acid on secretion in the proximal and distal rat colon and coordination of bowel movements in the guinea pig colon.

Methods

The short-circuit current from the mucosal strip of the proximal and distal rat colon was compared under control conditions after induction of secretion with deoxycholic acid (DCA) as well as after inhibition of secretion with indomethacin, 1,2-bis (o-aminophenoxy) ethane-N,N,N′,N′-tetra-acetic acid (an intracellular calcium chelator; BAPTA), and tetrodotoxin (TTX) using an Ussing chamber. Colonic pressure patterns were also evaluated in the extracted guinea pig colon during resting, DCA stimulation, and inhibition by TTX using a newly developed pressure-sensing artificial stool.

Results

The secretory response in the distal colon was proportionate to the concentration of DCA. Also, indomethacin, BAPTA, and TTX inhibited chloride secretion in response to DCA significantly (P < 0.05). However, these changes were not detected in the proximal colon. When we evaluated motility, we found that DCA induced an increase in luminal pressure at the proximal, middle, and distal sensors of an artificial stool simultaneously during the non-peristaltic period (P < 0.05). In contrast, during peristalsis, DCA induced an increase in luminal pressure at the proximal sensor and a decrease in pressure at the middle and distal sensors of the artificial stool (P < 0.05).

Conclusions

DCA induced a clear segmental difference in electrogenic secretion. Also, DCA induced a more powerful peristaltic contraction only during the peristaltic period.

Rice Bran and Probiotics Alter the Porcine Large Intestine and Serum Metabolomes for Protection against Human Rotavirus Diarrhea

Human rotavirus (HRV) is a leading cause of severe childhood diarrhea, and there is limited vaccine efficacy in the developing world. Neonatal gnotobiotic pigs consuming a prophylactic synbiotic combination of probiotics and rice bran (Pro+RB) did not exhibit HRV diarrhea after challenge. Multiple immune, gut barrier protective, and anti-diarrheal mechanisms contributed to the prophylactic efficacy of Pro+RB when compared to probiotics (Pro) alone. In order to understand the molecular signature associated with diarrheal protection by Pro+RB, a global non-targeted metabolomics approach was applied to investigate the large intestinal contents and serum of neonatal gnotobiotic pigs. The ultra-high performance liquid chromatography-tandem mass spectrometry platform revealed significantly different metabolites (293 in LIC and 84 in serum) in the pigs fed Pro+RB compared to Pro, and many of these metabolites were lipids and amino acid/peptides. Lipid metabolites included 2-oleoylglycerol (increased 293.40-fold in LIC of Pro+RB, p = 3.04E-10), which can modulate gastric emptying, andhyodeoxycholate (decreased 0.054-fold in the LIC of Pro+RB, p = 0.0040) that can increase colonic mucus production to improve intestinal barrier function. Amino acid metabolites included cysteine (decreased 0.40-fold in LIC, p = 0.033, and 0.62-fold in serum, p = 0.014 of Pro+RB), which has been found to reduce inflammation, lower oxidative stress and modulate mucosal immunity, and histamine (decreased 0.18-fold in LIC, p = 0.00030, of Pro+RB and 1.57-fold in serum, p = 0.043), which modulates local and systemic inflammatory responses as well as influences the enteric nervous system. Alterations to entire LIC and serum metabolic pathways further contributed to the anti-diarrheal and anti-viral activities of Pro+RB such as sphingolipid, mono/diacylglycerol, fatty acid, secondary bile acid, and polyamine metabolism. Sphingolipid and long chain fatty acid profiles influenced the ability of HRV to both infect and replicate within cells, suggesting that Pro+RB created a protective lipid profile that interferes with HRV activity. Polyamines act on enterocyte calcium-sensing receptors to modulate intracellular calcium levels, and may directly interfere with rotavirus replication. These results support that multiple host and probiotic metabolic networks, notably those involving lipid and amino acid/peptide metabolism, are important mechanisms through which Pro+RB protected against HRV diarrhea in neonatal gnotobiotic pigs.

Protective effects of β-casofensin, a bioactive peptide from bovine β-casein, against indomethacin-induced intestinal lesions in rats

SCOPE

β-casofensin, also known as peptide β-CN(94-123), is a milk bioactive peptide that modulates the intestinal barrier through its action on goblet cells. Here, we evaluated whether oral administration of β-casofensin can prevent indomethacin-induced injury of the jejunum in rats.

METHODS AND RESULTS

Rats received β-casofensin (0.01-100 μM) or tap water by daily gavage (4 μL/g) for eight days, then two subcutaneous injections of indomethacin (10 mg/kg, days 9 and 10) and were euthanized on day 12. In vitro, we investigated the effects of β-casofensin on the restitution of a wounded monolayer. Preventive administration of β-casofensin (100 μM) reduced intestinal macroscopic and microscopic damage induced by indomethacin. β-casofensin also prevented the depletion of goblet cells and increased myeloperoxidase activity, as well as tumor necrosis factor-ɑ (TNF-ɑ) expression and immunostaining of active caspase-3 in the jejunum of rats treated with indomethacin. In wound healing experiments, β-casofensin promoted epithelial restitution with no effect on cell proliferation. This effect was inhibited by pre-incubation with an anti-CC chemokine receptor 6 (CCR6) neutralizing antibody.

CONCLUSIONS

β-casofensin exerts protective effects in indomethacin-induced enteritis through preservation of goblet cells and improvement in wound healing. β-casofensin could therefore become vital in nutritional programs for the prevention of intestinal diseases.

Bile Acid diarrhea: prevalence, pathogenesis, and therapy

Bile acid diarrhea (BAD) is usually seen in patients with ileal Crohn’s disease or ileal resection. However, 25% to 50% of patients with functional diarrhea or diarrhea-predominant irritable bowel syndrome (IBS-D) also have evidence of BAD. It is estimated that 1% of the population may have BAD. The causes of BAD include a deficiency in fibroblast growth factor 19 (FGF-19), a hormone produced in enterocytes that regulates hepatic bile acid (BA) synthesis. Other potential causes include genetic variations that affect the proteins involved in BA enterohepatic circulation and synthesis or in the TGR5 receptor that mediates the actions of BA in colonic secretion and motility. BAs enhance mucosal permeability, induce water and electrolyte secretion, and accelerate colonic transit partly by stimulating propulsive high-amplitude colonic contractions. There is an increased proportion of primary BAs in the stool of patients with IBS-D, and some changes in the fecal microbiome have been described. There are several methods of diagnosing BAD, such as ⁷⁵selenium homotaurocholic acid test retention, serum C4, FGF-19, and fecal BA measurement; presently, therapeutic trials with BA sequestrants are most commonly used for diagnosis. Management involves the use of BA sequestrants including cholestyramine, colestipol, and colesevelam. FXR agonists such as obeticholic acid constitute a promising new approach to treating BAD.

Novel Therapies in IBS-D Treatment

OPINION STATEMENT

Irritable bowel syndrome (IBS) is a common gastrointestinal disease characterized by abdominal pain and change in bowel habits. IBS diarrhea predominant (IBS-D), which is arguably the most common subset of IBS, is also associated with rectal urgency, increased frequency, abdominal bloating, and loose to watery stools. Current treatments for diarrhea include mu-opioid agonists (i.e., loperamide, lomotil) and bile acid sequestrants (i.e., cholestyramine) while treatments for abdominal pain include antispasmodics (i.e., hyoscyamine, dicyclomine) and tricyclic antidepressants (i.e., amitriptyline). There are currently 3 FDA-approved treatments for IBS-D, which have been shown to improve both abdominal pain and diarrhea. Alosetron was initially approved by FDA 2000; however, its use is now limited to women with severe IBS-D symptoms refractory to other treatment. Eluxadoline, a mixed mu-opioid agonist, and rifaximin, a broad spectrum gut specific antibiotic, were both FDA approved in 2015. Eluxadoline has been shown to relieve abdominal pain and stool consistency in appropriate candidates. While large trials already showed the efficacy of rifaximin in treating non-constipated IBS for bloating, stool consistency, and abdominal pain, the recent TARGET 3 trial demonstrates that retreatment is also effective. While these new treatments significantly expand options for patients suffering from IBS-D, there is likely to remain a need for additional safe and effective therapies.

Sensitization to autoimmune hepatitis in group VIA calcium-independent phospholipase A2-null mice led to duodenal villous atrophy with apoptosis, goblet cell hyperplasia and leaked bile acids

Chronic bowel disease can co-exist with severe autoimmune hepatitis (AIH) in an absence of primary sclerosing cholangitis. Genetic background may contribute to this overlap syndrome. We previously have shown that the deficiency of iPLA2β causes an accumulation of hepatocyte apoptosis, and renders susceptibility for acute liver injury. We here tested whether AIH induction in iPLA2β-null mice could result in intestinal injury, and whether bile acid metabolism was altered. Control wild-type (WT) and female iPLA2β-null (iPLA2β(-/-)) mice were intravenously injected with 10mg/kg concanavalinA (ConA) or saline for 24h. ConA treatment of iPLA2β(-/-) mice caused massive liver injury with increased liver enzymes, fibrosis, and necrosis. While not affecting WT mice, ConA treatment of iPLA2β(-/-) mice caused severe duodenal villous atrophy concomitant with increased apoptosis, cell proliferation, globlet cell hyperplasia, and endotoxin leakage into portal vein indicating a disruption of intestinal barrier. With the greater extent than in WT mice, ConA treatment of iPLA2β(-/-) mice increased jejunal expression of innate response cytokines CD14, TNF-α, IL-6, and SOCS3 as well as chemokines CCL2 and the CCL3 receptor CCR5. iPLA2β deficiency in response to ConA-induced AIH caused a significant decrease in hepatic and biliary bile acids, and this was associated with suppression of hepatic Cyp7A1, Ntcp and ABCB11/Bsep and upregulation of intestinal FXR/FGF15 mRNA expression. The suppression of hepatic Ntcp expression together with the loss of intestinal barrier could account for the observed bile acid leakage into peripheral blood. Thus, enteropathy may result from acute AIH in a susceptible host such as iPLA2β deficiency.

Current and emerging drug options in the treatment of diarrhea predominant irritable bowel syndrome

INTRODUCTION

Irritable bowel syndrome diarrhea predominant (IBS-D) is a highly prevalent GI disease, affecting nearly a third of all patients diagnosed with irritable bowel syndrome. Current treatment options are limited.

AREAS COVERED

This review discusses the pharmacotherapeutic options for IBS-D including currently used medications, the two newly FDA approved medications, as well as emerging therapies with potential benefit in IBS-D. Particular emphasis is placed on rifaximin and eluxadoline and their possible use in IBS-D.

EXPERT OPINION

Current pharmacological treatment of IBS-D includes loperamide, bile acid sequestrants, antispasmodics, tricyclic antidepressants, alosetron, eluxadoline and rifaximin. The latter two treatments have significantly added to the pharmacotherapeutic options for patients suffering from IBS-D.

The role of bile acids in functional GI disorders

BACKGROUND

Bile acids are increasingly implicated in the pathogenesis of functional GI disorders. New mechanisms have recently been described in the irritable bowel syndrome, chronic diarrhea and chronic idiopathic constipation. Identification of bile acid signaling through farnesoid X receptor (FXR), transmembrane G-coupled receptor 5 (TGR5) and fibroblast growth factor 19 (FGF19) has led to the development of new, directly acting therapeutic agents. Despite these advances primary bile acid diarrhea remains under-recognized partly because of the lack of a widely available diagnostic test.

PURPOSE

In this review we will summarize the effects of bile acids on bowel function throughout the gastrointestinal tract and their roles in the pathogenesis of functional diseases. We will review established diagnostic tests and therapies for functional heartburn, dyspepsia and bile acid diarrhea. There will be a particular emphasis on recent trial data for emerging therapies such as Elobixibat and Obeticholic acid and novel diagnostic tests for bile acid diarrhea such as 7α-Hydroxy-4-cholesten-3-one (C4) and FGF19. Finally we will discuss future directions for research in this rapidly evolving field, such as bacterial bile acid modification and identification of genetic anomalies associated with functional disorders.

Pasture v. standard dairy cream in high-fat diet-fed mice: improved metabolic outcomes and stronger intestinal barrier

Dairy products derived from the milk of cows fed in pastures are characterised by higher amounts of conjugated linoleic acid and α-linolenic acid (ALA), and several studies have shown their ability to reduce cardiovascular risk. However, their specific metabolic effects compared with standard dairy in a high-fat diet (HFD) context remain largely unknown; this is what we determined in the present study with a focus on the metabolic and intestinal parameters. The experimental animals were fed for 12 weeks a HFD containing 20 % fat in the form of a pasture dairy cream (PDC) or a standard dairy cream (SDC). Samples of plasma, liver, white adipose tissue, duodenum, jejunum and colon were analysed. The PDC mice, despite a higher food intake, exhibited lower fat mass, plasma and hepatic TAG concentrations, and inflammation in the adipose tissue than the SDC mice. Furthermore, they exhibited a higher expression of hepatic PPARα mRNA and adipose tissue uncoupling protein 2 mRNA, suggesting an enhanced oxidative activity of the tissues. These results might be explained, in part, by the higher amounts of ALA in the PDC diet and in the liver and adipose tissue of the PDC mice. Moreover, the PDC diet was found to increase the proportions of two strategic cell populations involved in the protective function of the intestinal epithelium, namely Paneth and goblet cells in the small intestine and colon, compared with the SDC diet. In conclusion, a PDC HFD leads to improved metabolic outcomes and to a stronger gut barrier compared with a SDC HFD. This may be due, at least in part, to the protective mechanisms induced by specific lipids.

Farnesoid X receptor agonists attenuate colonic epithelial secretory function and prevent experimental diarrhoea in vivo

OBJECTIVE

Bile acids are important regulators of intestinal physiology, and the nuclear bile acid receptor, farnesoid X receptor (FXR), is emerging as a promising therapeutic target for several intestinal disorders. Here, we investigated a role for FXR in regulating intestinal fluid and electrolyte transport and the potential for FXR agonists in treating diarrhoeal diseases.

DESIGN

Electrogenic ion transport was measured as changes in short-circuit current across voltage-clamped T84 cell monolayers or mouse tissues in Ussing chambers. NHE3 activity was measured as BCECF fluorescence in Caco-2 cells. Protein expression was measured by immunoblotting and cell surface biotinylation. Antidiarrhoeal efficacy of GW4064 was assessed using two in vivo mouse models: the ovalbumin-induced diarrhoea model and cholera toxin (CTX)-induced intestinal fluid accumulation.

RESULTS

GW4064 (5 μmol/L; 24 h), a specific FXR agonist, induced nuclear translocation of the receptor in T84 cells and attenuated Cl(-) secretory responses to both Ca(2+) and cAMP-dependent agonists. GW4064 also prevented agonist-induced inhibition of NHE3 in Caco-2 cells. In mice, intraperitoneal administration of GW4064 (50 mg/mL) also inhibited Ca(2+) and cAMP-dependent secretory responses across ex vivo colonic tissues and prevented ovalbumin-induced diarrhoea and CTX-induced intestinal fluid accumulation in vivo. At the molecular level, FXR activation attenuated apical Cl(-) currents by inhibiting expression of cystic fibrosis transmembrane conductance regulator channels and inhibited basolateral Na(+)/K(+)-ATPase activity without altering expression of the protein.

CONCLUSIONS

These data reveal a novel antisecretory role for the FXR in colonic epithelial cells and suggest that FXR agonists have excellent potential for development as a new class of antidiarrheal drugs.

Bile acids in regulation of intestinal physiology

In addition to their roles in facilitating lipid digestion and absorption, bile acids are recognized as important regulators of intestinal function. Exposure to bile acids can dramatically influence intestinal transport and barrier properties; in recent years, they have also become appreciated as important factors in regulating cell growth and survival. Indeed, few cells reside within the intestinal mucosa that are not altered to some degree by exposure to bile acids. The past decade saw great advances in the knowledge of how bile acids exert their actions at the cellular and molecular levels. In this review, we summarize the current understanding of the role of bile acids in regulation of intestinal physiology.

Physiological concentrations of bile acids down-regulate agonist induced secretion in colonic epithelial cells

In patients with bile acid malabsorption, high concentrations of bile acids enter the colon and stimulate Cl(-) and fluid secretion, thereby causing diarrhoea. However, deoxycholic acid (DCA), the predominant colonic bile acid, is normally present at lower concentrations where its role in regulating transport is unclear. Thus, the current study set out to investigate the effects of physiologically relevant DCA concentrations on colonic epithelial secretory function. Cl(-) secretion was measured as changes in short-circuit current across voltage-clamped T(84) cell monolayers. At high concentrations (0.5-1 mM), DCA acutely stimulated Cl(-) secretion but this effect was associated with cell injury, as evidenced by decreased transepithelial resistance (TER) and increased lactate dehydrogenase (LDH) release. In contrast, chronic (24 hrs) exposure to lower DCA concentrations (10-200 microM) inhibited responses to Ca(2+) and cAMP-dependent secretagogues without altering TER, LDH release, or secretagogue-induced increases in intracellular second messengers. Other bile acids - taurodeoxycholic acid, chenodeoxycholic acid and cholic acid - had similar antisecretory effects. DCA (50 microM) rapidly stimulated phosphorylation of the epidermal growth factor receptor (EGFr) and both ERK and p38 MAPKs (mitogen-activated protein kinases). The EGFr inhibitor, AG1478, and the protein synthesis inhibitor, cycloheximide, reversed the antisecretory effects of DCA, while the MAPK inhibitors, PD98059 and SB203580, did not. In summary, our studies suggest that, in contrast to its acute prosecretory effects at pathophysiological concentrations, lower, physiologically relevant, levels of DCA chronically down-regulate colonic epithelial secretory function. On the basis of these data, we propose a novel role for bile acids as physiological regulators of colonic secretory capacity.

Novel localization of Rab3D in rat intestinal goblet cells and Brunner's gland acinar cells suggests a role in early Golgi trafficking

Rab3D is a small GTP-binding protein that associates with secretory granules of endocrine and exocrine cells. The physiological role of Rab3D remains unclear. While it has initially been implicated in the control of regulated exocytosis, recent deletion-mutation studies have suggested that Rab3D is involved in the biogenesis of secretory granules. Here, we report the unexpected finding that Rab3D also associates with early Golgi compartments in intestinal goblet cells and in Brunner's gland acinar cells. Expression of Rab3D in the intestine was demonstrated by SDS-PAGE and Western blot analysis of homogenates prepared from the rat duodenum and colon. Confocal laser scanning microscopy revealed Rab3D immunofluorescence in the Golgi area of goblet cells of the duodenum and colon and in Brunner's gland acinar cells. There was no colocalization between Rab3D and a trans-Golgi network marker, TGN-38. In contrast, Rab3D colocalized partially with a cis-Golgi marker, GM-130, and with a marker of cis-Golgi and coat protein complex I vesicles, beta-COP. Strong colocalization was observed between Rab3D and the lectins Griffonia simplicifolia agglutinin II and soybean agglutinin, which have been described as markers of the medial and cis-Golgi, respectively. Rabphilin, a putative effector of Rab3D, displayed an identical pattern of Golgi localization. Incubation of colon tissue with carbamylcholine or deoxycholate to stimulate exocytosis by goblet cells caused a partial redistribution of Rab3D to the cytoplasm and mucous granule field and a concomitant transformation of the Golgi architecture. Taken together, the present data suggest that Rab3D and rabphilin may regulate the secretory pathway at a much earlier stage than what has hitherto been assumed.

Transcriptional regulation of human mucin MUC4 by bile acids in oesophageal cancer cells is promoter-dependent and involves activation of the phosphatidylinositol 3-kinase signalling pathway

Abnormal gastro-oesophageal reflux and bile acids have been linked to the presence of Barrett's oesophageal premalignant lesion associated with an increase in mucin-producing goblet cells and MUC4 mucin gene overexpression. However, the molecular mechanisms underlying the regulation of MUC4 by bile acids are unknown. Since total bile is a complex mixture, we undertook to identify which bile acids are responsible for MUC4 up-regulation by using a wide panel of bile acids and their conjugates. MUC4 apomucin expression was studied by immunohistochemistry both in patient biopsies and OE33 oesophageal cancer cell line. MUC4 mRNA levels and promoter regulation were studied by reverse transcriptase-PCR and transient transfection assays respectively. We show that among the bile acids tested, taurocholic, taurodeoxycholic, taurochenodeoxycholic and glycocholic acids and sodium glycocholate are strong activators of MUC4 expression and that this regulation occurs at the transcriptional level. By using specific pharmacological inhibitors of mitogen-activated protein kinase, phosphatidylinositol 3-kinase, protein kinase A and protein kinase C, we demonstrate that bile acid-mediated up-regulation of MUC4 is promoter-specific and mainly involves activation of phosphatidylinositol 3-kinase. This new mechanism of regulation of MUC4 mucin gene points out an important role for bile acids as key molecules in targeting MUC4 overexpression in early stages of oesophageal carcinogenesis.