Effects of butyrate on active sodium and chloride transport in rat and rabbit distal colon

Mechanisms and emerging strategies for irinotecan-induced diarrhea

Irinotecan (also known as CPT-11) is a topoisomerase I inhibitor first approved for clinical use as an anticancer agent in 1996. Over the past more than two decades, it has been widely used for combination regimens to treat various malignancies, especially in gastrointestinal and lung cancers. However, severe dose-limiting toxicities, especially gastrointestinal toxicity such as late-onset diarrhea, were frequently observed in irinotecan-based therapy, thus largely limiting the clinical application of this agent. Current knowledge regarding the pathogenesis of irinotecan-induced diarrhea is characterized by the complicated metabolism of irinotecan to its active metabolite SN-38 and inactive metabolite SN-38G. A series of enzymes and transporters were involved in these metabolic processes, including UGT1A1 and CYP3A4. Genetic polymorphisms of these metabolizing enzymes were significantly associated with the occurrence of irinotecan-induced diarrhea. Recent discoveries and progress made on the detailed mechanisms enable the identification of potential biomarkers for predicting diarrhea and as such guiding the proper patient selection with a better range of tolerant dosages. In this review, we introduce the metabolic process of irinotecan and describe the pathogenic mechanisms underlying irinotecan-induced diarrhea. Based on the mechanisms, we further outline the potential biomarkers for predicting the severity of diarrhea. Finally, based on the current experimental evidence in preclinical and clinical studies, we discuss and prospect the current and emerging strategies for the prevention of irinotecan-induced diarrhea.

Insight into role of short chain fatty acids in regulating intestinal mucosal barrier and alleviating inflammatory bowel disease

In recent years, the importance of intestinal microbiota and its metabolites in maintaining the human intestinal environment has been gradually revealed. Therefore, short chain fatty acids (SCFAs), as the metabolites produced by the intestinal microbiota, play a momentous part in regulating the balance between the function and morphology of the mucosal barrier, regulating the proliferation and differentiation of mucosal cells, protecting the integrity and permeability of the mucosal barrier, and maintainingthe stability of tight junctions. Inflammatory bowel disease (IBD) is a chronic, inflammatory condition of the gastrointestinal tract, associated with a disturbance of intestinal barrier function and dysregulation of the intestinal immune responses, the etiology and pathogenesis of which, however, are not yet fully uncovered. Animal models and human studies have corroborated the contribution of SCFAs in enhancing the barrier function through protective effects. This review will summarize the potential role of SCFAs in IBD with regard to regulating intestinal function, hoping to provide a new target for clinical treatment of IBD.

The impact of Morus alba L. leaf extract on intestinal ion transport. An in vitro study

Morus alba L. (White mulberry), is an important and popular herbal plant of the Moraceae family. It has been widely used due to its therapeutic properties, which include antidiabetic, antibacterial, anti-inflammatory, cardiovascular, and hypolpidemic activity. The present study evaluates the effects of aqueous white mulberry leaf extract on the transepithelial ion pathway in the rabbit colon epithelium (n = 48), using electrophysiological methods. In addition, the antioxidant potential and the chemical composition of the extract were determined. A mechanical-chemical stimulation with white mulberry in RH fluid (MB-RH) caused a statistically significant (p < 0.001) increase in the transepithelial electrical potential difference, from - 0.130 to - 0.685 mV. Gentle washing of the intestine with white mulberry in bumetanide, used as inhibitor of transepithelial chloride pathways, resulted in 14.8% shorter reaction than during MB-RH stimulation. There were no statistically significant differences between the electric potential values measured during stimulation with amiloride solution, used as inhibitor of transepithelial sodium pathways, and white mulberry in amilorid solution (p = 0.485). A short-term application of extract to the colon epithelium is responsible for local and reversible inhibition of chloride ion channels. The extract enhances sodium ion absorption and consequently changes the electrical potential. The effect of white mulberry extract on sodium ion transport may be related to the mechanism of hypoglycaemic activity of mulberry leaves.

The microbiota-gut-kidney axis mediates host osmoregulation in a small desert mammal

Regulating sodium and water balances is crucial for survival of small, desert mammals. Studies demonstrate that the gut microbiota and their metabolites are involved in host energy homeostasis, but little is known on the interactions among salt loading, gut microbiota, and osmoregulation. The aim of this study was to fill this gap. Mongolian gerbils (Meriones unguiculatus) were offered drinking water (Con) and either water containing moderate (4%, MS) or high NaCl (8%, HS) ad libitum. Intake of HS reduced α diversity of the microbial community and, at the genus level, reduced the relative abundances of Rikenella and Christensenella but increased Atopobium. To confirm the function of gut microbiota in host osmoregulation, we transplanted caecal microbiota in HS gerbils. To cope with salt loading, the gerbils concentrated urine, resulting in negative energy balance and systemic inflammation. The HS gerbils increased hypothalamic arginine vasopressin and intestinal and renal aquaporin 2 to support water retention, and reduced intestinal and renal epithelial sodium channel α to promote sodium excretion. However, HS gerbils with caecal microbiota transplant (CMT) from Con donors maintained energy balance and osmoregulation, and had a much reduced systemic inflammation. Further, CMT from Con donors to HS recipients reshaped the gut microbiota, particularly by reducing Parabacteroides distasonis and Prevotella copri, and increasing Lactobacillus reuteri abundances, with a resulting increase in bacterial metabolites such as butyrate. These findings highlight a vital role of the microbiota-gut-kidney axis in mediating salt-related osmoregulation, allowing small mammals to adapt to high salt loads in a desert habitat.

The Role of Gut Microbiota and Metabolites in Obesity-Associated Chronic Gastrointestinal Disorders

The gut microbiota is a complex community of microorganisms that has become a new focus of attention due to its association with numerous human diseases. Research over the last few decades has shown that the gut microbiota plays a considerable role in regulating intestinal homeostasis, and disruption to the microbial community has been linked to chronic disease conditions such as inflammatory bowel disease (IBD), colorectal cancer (CRC), and obesity. Obesity has become a global pandemic, and its prevalence is increasing worldwide mostly in Western countries due to a sedentary lifestyle and consumption of high-fat/high-sugar diets. Obesity-mediated gut microbiota alterations have been associated with the development of IBD and IBD-induced CRC. This review highlights how obesity-associated dysbiosis can lead to the pathogenesis of IBD and CRC with a special focus on mechanisms of altered absorption of short-chain fatty acids (SCFAs).

A Funnel-Shaped Chloride Nanochannel Inspired By ClC Protein

Chloride transport participates in a great variety of physiological activities, such as regulating electrical excitability and maintaining acid-base equilibrium. However, the high flux is the prerequisite to ensure the realization of the above functions. Actually, the high flux of ion transport is significant, not only for living things but also for practical applications. Herein, inspired by chloride channel (ClC) protein, a novel NH₂-pillar[5]arene functionalized funnel-shaped nanochannel was designed and constructed. The introduction of functional molecules changed surface charge property and endowed the nanochannel with Cl^- selectivity, which facilitated Cl^- transport. Moreover, by adjusting the asymmetric degree of the nanochannel, the Cl^- transport flux can be improved greatly. The successful construction of an artificial ion channel with high flux will be much useful for practical applications like microfluidic devices, sensors, and ion separation.

Prediction of Postoperative Ileus in Patients With Colorectal Cancer by Preoperative Gut Microbiota

Background

Ileus and postoperative ileus (POI) are common complications of colorectal cancer (CRC). However, little is known about the gut microbiota associated with ileus.

Method

Differences in gut microbiota were evaluated by 16S rRNA gene sequencing. We characterized the gut microbiota in 85 CRC patients (cohort 1) and detected differences, and an independent cohort composed of 38 CRC patients (cohort 2) was used to evaluate the results.

Results

The gut microbiota of CRC patients with and without ileus exhibited large differences in alpha- and beta-diversities and bacterial taxa. The Firmicutes-to-Bacteroidetes ratio and microbial dysbiosis index (MDI) showed greater dysbiosis among ileus patients than among those without ileus. According to the location of CRC, the difference in gut microbiota between patients with and without ileus was more obvious in those with distal CRC than in those with proximal CRC. Finally, Faecalibacterium was significantly reduced in the postoperative perioperative period in patients with ileus. Thus, we used Faecalibacterium as a biomarker for predicting perioperative or POI: the AUC value was 0.74 for perioperative ileus and 0.67 for POI that appeared at 6 months after hospital discharge. The predictive power was evaluated in Cohort 2, with an AUC value of 0.79.

Conclusion

These findings regarding difference of gut microbiota in postoperative CRC patients may provide a theoretical basis for the use of microbiota as biomarkers for the prediction of POI.

Lactose-Induced Chronic Diarrhea Results From Abnormal Luminal Microbial Fermentation and Disorder of Ion Transport in the Colon

Diarrhea is one of the major abdominal symptoms in lactose-intolerant subjects. The changes in the large intestinal luminal environment and disorder of the epithelial ion transport in lactose-induced diarrhea remain unclear. The present study aimed to investigate the effect of an incremental high-lactose diet (IHLD, 30%/40%/50%) on luminal microbiota, microbiota-derived metabolite concentrations and colonic ion transport. Gut microbiota were analyzed by 16S rRNA amplicon sequencing and the concentration of SCFAs by gas chromatography, galactose, lactose and lactic acid through assay kit; Ussing chamber was performed to detect basal and stimulated ion transport; The expression and location of SCFA transporters, the Na-H exchanger 3(NHE3), cystic fibrosis transporter regulater (CFTR) and NKCC1 in the colon mucosa were analyzed by western and immunostaining. The concentrations of lactose, galactose and lactic acid of the cecal content were markedly increased (P < 0.01) and SCFA concentration was significantly decreased (P < 0.01). This was associated with depletion of the Lachnospiraceae NK4A136 group and Ruminococcaceae UCG-005 and increased relative abundance of Lactobacillus, escherichia-shigella and megamonas in the cecal microbiota. The expression of monocarboxylate transporter 1 was decreased in the colonic mucosa of the IHLD group. Low NHE3 expression and phosphorylation levels, and decreases in delta basal short circuit current after apical Na⁺ removal in the colonic mucosa of the IHLD group contributed to Na⁺ accumulation in the lumen and decrease stimulated Cl^– secretion with low CFTR and NKCC1 expression would compensate for water and electrolyte loss during the diarrhea process. These results indicated that the persistence of the diarrhea state was maintained by abnormal colonic microbiota fermentation leading to high concentrations of lactose, galactose and lactic acid and low SCFAs in the lumen, and decreased Na⁺ absorption with the low NHE3 expression and phosphorylation levels.

Short Chain Fatty Acids Effect on Chloride Channel ClC-2 as a Possible Mechanism for Lubiprostone Intestinal Action

Lubiprostone, a 20-carbon synthetic fatty acid used for the treatment of constipation, is thought to act through an action on Cl⁻ channel ClC-2. Short chain fatty acids (SCFAs) are produced and absorbed in the distal intestine. We explore whether SCFAs affect ClC-2, re-examine a possible direct effect of lubiprostone on ClC-2, and use mice deficient in ClC-2 to stringently address the hypothesis that the epithelial effect of lubiprostone targets this anion channel. Patch-clamp whole cell recordings of ClC-2 expressed in mammalian cells are used to assay SCFA and lubiprostone effects. Using chamber measurements of ion current in mice deficient in ClC-2 or CFTR channels served to analyze the target of lubiprostone in the distal intestinal epithelium. Intracellular SCFAs had a dual action on ClC-2, partially inhibiting conduction but, importantly, facilitating the voltage activation of ClC-2. Intra- or extracellular lubiprostone had no effect on ClC-2 currents. Lubiprostone elicited a secretory current across colonic epithelia that was increased in mice deficient in ClC-2, consistent with the channel’s proposed proabsorptive function, but absent from those deficient in CFTR. Whilst SCFAs might exert a physiological effect on ClC-2 as part of their known proabsorptive effect, ClC-2 plays no part in the lubiprostone intestinal effect that appears mediated by CFTR activation.

Adhesive Bifidobacterium Induced Changes in Cecal Microbiome Alleviated Constipation in Mice

Constipation, which seriously affects living quality of people, is a common gastrointestinal disease. The engagement of the intestinal flora in the development of symptoms of constipation has been frequently hypothesized. In this study, constipated mice induced by loperamide were used to investige the alleviation of constipation by Bifidobacteria. Bifidobacteria was sorted out according to their adhesive properties into two groups. One group combined multiple strains of Bifidobacterium with adhesion property (CMB1), the other combined multiple strains of Bifidobacterium without adhesion property (CMB2). It was found that CMB1 can alleviate constipation more efficiently by improving the water, propionate and butyrate content in feces, and overall gastrointestinal transit time. Meanwhile, from the perspective of fecal microbiota, CMB1 alleviated constipation mainly by increasing the relative abundances of genera (Bifidobacterium, Lactobacillus, and Prevotella) associated with rapid bowel movement. From the perspective of cecal microbiota, CMB1 alleviated constipation mainly by increasing the relative abundances of genera Lactobacillus, Bacteroides, unclassified S24-7, Dorea, Ruminococcus, Coprococcus, and Rikenella, and decreasing the relative abundances of genera Oscillospira, Odoribacter and Unclassified F16, which are associated with methane production and colonic transit. Overall, changes of microbiota in caecum by CMB1 reflect the stage of constipation in mice more comprehensively than that in feces.

Expression, Localization and Functional Activity of the Major Na⁺/H⁺ Exchange Isoforms Expressed in the Intestinal Cell Line Caco-2BBe

Background/Aims

Enterocytes express a number of NHE isoforms with presumed localization in the apical (NHE2, 3 and 8) or basolateral (NHE1) membrane. Functional activity and localization of enterocyte NHE isoforms were assessed using fully differentiated Caco-2BBe cells, whose genetic expression profile closely resembles mature enterocytes.

Methods

The activity of the different NHEs was analyzed by fluorometric pH_i-metry in a perfusion chamber with separate apical and basolateral perfusion, using specific inhibitors and shRNA knockdown of NHE2. The expression of the NHEs and of other relevant acid extrusion transporters was quantified by qPCR.

Results

Quantitative comparison of the mRNA expression levels of the different NHE isoforms in 14 day-differentiated Caco-2BBe cells showed the following order: NHE2>NHE8>NHE3>NHE1. Acid-activated NHE exchange rates in the basolateral membrane were >6-fold higher than in the apical membrane. 79 ± 3 % of the acid-activated basolateral Na⁺/H⁺ exchange rate displayed a NHE1-typical inhibitor profile, and no NHE2/3/8 typical activity could be observed. Analysis of the apical Na⁺/H⁺ exchange rates revealed that approximately 51 ± 3 % of the total apical activity displayed a NHE2/8-typical inhibitor profile and 31 ± 6 % a NHE3-typical inhibitor profile. Because no selective NHE2 inhibitor is available, a stable NHE2 knockdown cell line (C2NHE2KD) was generated. C2NHE2KD displayed a reduced NHE2-typical apical Na⁺/H⁺ exchange rate and maintained a lower steady-state pH_i, despite high expression levels of other acid extruders, in particular NBCn1 (Slc4a7).

Conclusion

Differentiated Caco-2BBe cells display particularly high mRNA expression levels of NHE2, which can be functionally identified in the apical membrane. Although at low intracellular pH, NHE2 transport rate was far lower than that of NHE1. NHE2 activity was nevertheless essential for the maintenance of the steady-state pH_i of these cells.

Antidiarrheal Action of Bacillus subtilis CU1 CNCM I-2745 and Lactobacillus plantarum CNCM I-4547 in Mice

Preventive actions of probiotics as antidiarrheal agents are well documented, but their mechanisms are poorly understood. Two selected probiotics, Bacillus subtilis CU1 and Lactobacillus plantarum CNCM I-4547, were tested in mouse experimental models of diarrhea and the possible mechanisms of action were investigated. Diarrhea was induced in mice by oral castor oil administration or by i.v. injection of lipopolysaccharide (LPS) of Salmonella enteritis. The antidiarrheal drug loperamide was used as control. Fecal water excretion was quantified for 2 h and paracellular permeability and electrical parameters of the colon were assessed in Ussing chambers. The expression of colonic exchangers or channels and of Toll-like receptor 4 (TLR4) was assessed by immunohistochemistry. Prophylactic treatment with B. subtilis CU1 or with L. plantarum CNCM I-4547 reduced LPS-induced diarrhea. The reduction of water excretion was in the same range as those induced by loperamide. In the castor oil model, this effect was only observed with B. subtilis CU1. The two probiotic treatments abolished the increase in paracellular permeability induced by LPS, but not by castor oil. However, only L. plantarum CNCM I-4547 treatment decreased the colonic expression of TLR-4. After B. subtilis CU1, colonic expression of cystic fibrosis transmembrane conductance regulator (CFTR) was reduced and that of Na⁺/H⁺ exchanger 3 (NHE3) increased. B. subtilis CU1 may increase the capacity of the colon to absorb excess of water in diarrheic conditions by acting on CFTR and NHE3 expression. The two probiotics strains showed an impact on diarrhea through limitation of water excretion that may involve paracellular permeability or electrolyte transport for L. plantarum CNCM I-4547 and B. subtilis CU1 respectively.

Treatment of severe cholera: a review of strategies to reduce stool output and volumes of rehydration fluid

Background

Severe cholera is a life-threatening illness of hypovolemic shock and metabolic acidosis due to rapid and profuse diarrheal fluid loss. Emergency life-saving therapy is i.v. saline, optionally supplemented with potassium and alkali to correct the fluid deficit, potassium losses and acidosis. After this initial rehydration, for the next 2 days ongoing stool losses are replaced with oral rehydration solution (ORS), which contains sodium chloride, potassium and alkali together with glucose or rice powder as a source of glucose to serve as a carrier for sodium.

Results

In actual field trials, antibiotics are given to reduce fluid requirements, but large volumes averaging about 7 liters of i.v. fluid followed by about 14 liters of ORS have been given to adult patients. Disturbing trends during therapy have included overhydration, hyponatremia and polyuria.

Conclusions

It is suggested that stool output and fluid requirements could be reduced, if borne out in future research, by avoiding overhydration by restricting ORS intake to match stool output and promoting intestinal reabsorption of luminal fluid by early introduction of glucose without salts into the intestine, more gradual correction of dehydration, giving mineralocorticoid and vasopressin, and infusing glucose or short-chain fatty acids into the proximal colon.

Effects of aqueous extracts from Ceratonia siliqua L. pods on small intestinal motility in rats and jejunal permeability in mice

The current study was performed to assess the effects of carob pod aqueous extracts (CPAE, pulp, seeds or mixture) on gastrointestinal transit (GIT) and intestinal epithelium permeability.

Na-H Exchanger Isoform-2 (NHE2) Mediates Butyrate-dependent Na+ Absorption in Dextran Sulfate Sodium (DSS)-induced Colitis

Diarrhea associated with ulcerative colitis (UC) occurs primarily as a result of reduced Na(+) absorption. Although colonic Na(+) absorption is mediated by both epithelial Na(+) channels (ENaC) and Na-H exchangers (NHE), inhibition of NHE-mediated Na(+) absorption is the primary cause of diarrhea in UC. As there are conflicting observations reported on NHE expression in human UC, the present study was initiated to identify whether NHE isoforms (NHE2 and NHE3) expression is altered and how Na(+) absorption is regulated in DSS-induced inflammation in rat colon, a model that has been used to study UC. Western blot analyses indicate that neither NHE2 nor NHE3 expression is altered in apical membranes of inflamed colon. Na(+) fluxes measured in vitro under voltage clamp conditions in controls demonstrate that both HCO3 (-)-dependent and butyrate-dependent Na(+) absorption are inhibited by S3226 (NHE3-inhibitor), but not by HOE694 (NHE2-inhibitor) in normal animals. In contrast, in DSS-induced inflammation, butyrate-, but not HCO3 (-)-dependent Na(+) absorption is present and is inhibited by HOE694, but not by S3226. These observations indicate that in normal colon NHE3 mediates both HCO3 (-)-dependent and butyrate-dependent Na(+) absorption, whereas DSS-induced inflammation activates NHE2, which mediates butyrate-dependent (but not HCO3 (-)-dependent) Na(+) absorption. In in vivo loop studies HCO3 (-)-Ringer and butyrate-Ringer exhibit similar rates of water absorption in normal rats, whereas in DSS-induced inflammation luminal butyrate-Ringer reversed water secretion observed with HCO3 (-)-Ringer to fluid absorption. Lumen butyrate-Ringer incubation activated NHE3-mediated Na(+) absorption in DSS-induced colitis. These observations suggest that the butyrate activation of NHE2 would be a potential target to control UC-associated diarrhea.

Oral rehydration therapy in the second decade of the twenty-first century

Oral rehydration solution (ORS) was established as the cornerstone of therapy for dehydration secondary to acute infectious diarrhea approximately 40 years ago. The efficacy of ORS is based on the ability of glucose to stimulate Na and fluid absorption in the small intestine via a cyclic AMP-independent process. Despite the establishment that ORS is the primary reason for the substantial reduction in morbidity and mortality from diarrhea in children in developing countries, the use of ORS has lagged for many reasons. This review highlights efforts to establish a major reformulation of ORS following the demonstration that short-chain fatty acids (SCFA) stimulate colonic Na and fluid absorption by a cyclic AMP-independent mechanism. The addition of high-amylose maize starch (HAMS), a microbially-fermentable (or 'resistant') starch, to ORS results in delivery of non-absorbed carbohydrate to the colon where it is fermented to SCFA. To date, three randomized controlled trials with a HAMS-ORS in south India have demonstrated a substantial decrease in diarrhea duration in both adults and children hospitalized for acute diarrhea. Significant efforts are now underway to establish this dual-action, modified HAMS-hypoosmolar ORS solution as the standard ORS for the treatment of dehydration from acute diarrhea.

Zinc sensing receptor signaling, mediated by GPR39, reduces butyrate-induced cell death in HT29 colonocytes via upregulation of clusterin

Zinc enhances epithelial proliferation, protects the digestive epithelial layer and has profound antiulcerative and antidiarrheal roles in the colon. Despite the clinical significance of this ion, the mechanisms linking zinc to these cellular processes are poorly understood. We have previously identified an extracellular Zn²⁺ sensing G-protein coupled receptor (ZnR) that activates Ca²⁺ signaling in colonocytes, but its molecular identity as well as its effects on colonocytes' survival remained elusive. Here, we show that Zn²⁺, by activation of the ZnR, protects HT29 colonocytes from butyrate induced cell death. Silencing of the G-protein coupled receptor GPR39 expression abolished ZnR-dependent Ca²⁺ release and Zn²⁺-dependent survival of butyrate-treated colonocytes. Importantly, GPR39 also mediated ZnR-dependent upregulation of Na⁺/H⁺ exchange activity as this activity was found in native colon tissue but not in tissue obtained from GPR39 knock-out mice. Although ZnR-dependent upregulation of Na⁺/H⁺ exchange reduced the cellular acid load induced by butyrate, it did not rescue HT29 cells from butyrate induced cell death. ZnR/GPR39 activation however, increased the expression of the anti-apoptotic protein clusterin in butyrate-treated cells. Furthermore, silencing of clusterin abolished the Zn²⁺-dependent survival of HT29 cells. Altogether, our results demonstrate that extracellular Zn²⁺, acting through ZnR, regulates intracellular pH and clusterin expression thereby enhancing survival of HT29 colonocytes. Moreover, we identify GPR39 as the molecular moiety of ZnR in HT29 and native colonocytes.

Tight junction defects in patients with atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is characterized by dry skin and a hyperactive immune response to allergens, 2 cardinal features that are caused in part by epidermal barrier defects. Tight junctions (TJs) reside immediately below the stratum corneum and regulate the selective permeability of the paracellular pathway.

OBJECTIVE

We evaluated the expression/function of the TJ protein claudin-1 in epithelium from AD and nonatopic subjects and screened 2 American populations for single nucleotide polymorphisms in the claudin-1 gene (CLDN1).

METHODS

Expression profiles of nonlesional epithelium from patients with extrinsic AD, nonatopic subjects, and patients with psoriasis were generated using Illumina's BeadChips. Dysregulated intercellular proteins were validated by means of tissue staining and quantitative PCR. Bioelectric properties of epithelium were measured in Ussing chambers. Functional relevance of claudin-1 was assessed by using a knockdown approach in primary human keratinocytes. Twenty-seven haplotype-tagging SNPs in CLDN1 were screened in 2 independent populations with AD.

RESULTS

We observed strikingly reduced expression of the TJ proteins claudin-1 and claudin-23 only in patients with AD, which were validated at the mRNA and protein levels. Claudin-1 expression inversely correlated with T(H)2 biomarkers. We observed a remarkable impairment of the bioelectric barrier function in AD epidermis. In vitro we confirmed that silencing claudin-1 expression in human keratinocytes diminishes TJ function while enhancing keratinocyte proliferation. Finally, CLDN1 haplotype-tagging SNPs revealed associations with AD in 2 North American populations.

CONCLUSION

Collectively, these data suggest that an impairment in tight junctions contributes to the barrier dysfunction and immune dysregulation observed in AD subjects and that this may be mediated in part by reductions in claudin-1.

Tight junction defects in patients with atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is characterized by dry skin and a hyperactive immune response to allergens, 2 cardinal features that are caused in part by epidermal barrier defects. Tight junctions (TJs) reside immediately below the stratum corneum and regulate the selective permeability of the paracellular pathway.

OBJECTIVE

We evaluated the expression/function of the TJ protein claudin-1 in epithelium from AD and nonatopic subjects and screened 2 American populations for single nucleotide polymorphisms in the claudin-1 gene (CLDN1).

METHODS

Expression profiles of nonlesional epithelium from patients with extrinsic AD, nonatopic subjects, and patients with psoriasis were generated using Illumina's BeadChips. Dysregulated intercellular proteins were validated by means of tissue staining and quantitative PCR. Bioelectric properties of epithelium were measured in Ussing chambers. Functional relevance of claudin-1 was assessed by using a knockdown approach in primary human keratinocytes. Twenty-seven haplotype-tagging SNPs in CLDN1 were screened in 2 independent populations with AD.

RESULTS

We observed strikingly reduced expression of the TJ proteins claudin-1 and claudin-23 only in patients with AD, which were validated at the mRNA and protein levels. Claudin-1 expression inversely correlated with T(H)2 biomarkers. We observed a remarkable impairment of the bioelectric barrier function in AD epidermis. In vitro we confirmed that silencing claudin-1 expression in human keratinocytes diminishes TJ function while enhancing keratinocyte proliferation. Finally, CLDN1 haplotype-tagging SNPs revealed associations with AD in 2 North American populations.

CONCLUSION

Collectively, these data suggest that an impairment in tight junctions contributes to the barrier dysfunction and immune dysregulation observed in AD subjects and that this may be mediated in part by reductions in claudin-1.

Role of colonic short-chain fatty acid transport in diarrhea

Short-chain fatty acids (SCFA) are the major anion in stool and are synthesized from nonabsorbed carbohydrate by the colonic microbiota. Nonabsorbed carbohydrate are not absorbed in the colon and induce an osmotically mediated diarrhea; in contrast, SCFA are absorbed by colonic epithelial cells and stimulate Na-dependent fluid absorption via a cyclic AMP-independent process involving apical membrane Na-H, SCFA-HCO(3), and Cl-SCFA exchanges. SCFA production represents an adaptive process to conserve calories, fluid, and electrolytes. Inhibition of SCFA synthesis by antibiotics and administration of PEG, a substance that is not metabolized by colonic microbiota, both result in diarrhea. In contrast, increased production of SCFA as a result of providing starch that is relatively resistant to amylase digestion [so-called resistant starch (RS)] to oral rehydration solution (RS-ORS) improves the efficacy of ORS and represents an important approach to improve the effectiveness of ORS in the treatment of acute diarrhea in children under five years of age.

Differential regulation of cholera toxin-inhibited Na-H exchange isoforms by butyrate in rat ileum

Electroneutral Na absorption occurs in the intestine via sodium-hydrogen exchanger (NHE) isoforms NHE2 and NHE3. Bicarbonate and butyrate both stimulate electroneutral Na absorption through NHE. Bicarbonate- but not butyrate-dependent Na absorption is inhibited by cholera toxin (CT). Long-term exposure to butyrate also influences expression of apical membrane proteins in epithelial cells. These studies investigated the effects of short- and long-term in vivo exposure to butyrate on apical membrane NHE and mRNA, protein expression, and activity in rat ileal epithelium that had been exposed to CT. Ileal loops were exposed to CT in vivo for 5 h and apical membrane vesicles were isolated. 22Na uptake was measured by using the inhibitor HOE694 to identify NHE2 and NHE3 activity, and Western blot analyses were performed. CT reduced total NHE activity by 70% in apical membrane vesicles with inhibition of both NHE2 and NHE3. Reduced NHE3 activity and protein expression remained low following removal of CT but increased to control values following incubation of the ileal loop with butyrate for 2 h. In parallel there was a 40% decrease in CT-induced increase in cAMP content. In contrast, NHE2 activity partially increased following removal of CT and was further increased to control levels by butyrate. NHE2 protein expression did not parallel its activity. Neither NHE2 nor NHE3 mRNA content were affected by CT or butyrate. These results indicate that CT has varying effects on the two apical NHE isoforms, inhibiting NHE2 activity without altering its protein expression and reducing both NHE3 activity and protein expression. Butyrate restores both CT-inhibited NHE2 and NHE3 activities to normal levels but via different mechanisms.

Expression of the short-chain fatty acid receptor, GPR43, in the human colon

Short-chain fatty acids (SCFAs), 2-4 carbon monocarboxylates including acetate, propionate and butyrate, are known to have a variety of physiological and pathophysiological effects on the intestine. Previously, we reported that the SCFA receptor, G-protein coupled receptor 43 (GPR43), is expressed by enteroendocrine and mucosal mast cells in the rat intestine. In the present study, expression and localization of GPR43 were investigated in the human large intestine. Gene and protein expression of GPR43 in the human ascending colon was analyzed by reverse transcriptase/polymerase chain reaction and Western blotting, respectively. In addition, localization of GPR43 was investigated by immunohistochemistry. In RT-PCR analysis, GPR43 mRNA was detected in whole wall mRNA samples. Western blotting analysis revealed the expression of GPR43 protein in whole wall and scraped mucosa protein samples, but not in muscle or submucosa. GPR43 immunoreactivity was observed in the intracellularly in enterocytes and in the peptide YY-immunoreactive enteroendocrine cells. These results indicate that the short chain fatty acid receptor, GPR43 is expressed by enteroendocrine L cells containing peptide YY in the human large intestine.

Acute inflammation alters bicarbonate transport in mouse ileum

T-cell mediated acute inflammation of the ileum may occur during Crohn's disease exacerbations. During ileal inflammation, absorption of nutrients and electrolytes by villus cells is decreased with a concomitant increase in crypt and/or villus fluid secretion. These alterations lead to fluid accumulation and the subsequent diarrhoea. Net intestinal fluid secretion consists of HCO3--rich plasma-like fluid. However, the regulation and mechanisms of HCO3- secretion in normal and acutely inflamed ileum are not clearly understood. To study this phenomenon, anti-CD3 monoclonal antibody (mAb)- induced in vivo ileal inflammatory mouse models was used for in vitro functional studies with Ussing chamber and pH stat techniques. Three hours after anti-CD3 mAb injection, ileal mucosa stripped of muscular and serosal layers showed a significant increase in short circuit current (Isc) (0.58+/-0.07 microEq h(-1) cm2 versus 1.63+/-0.14 microEq h(-1) cm2). The cAMP-stimulated Isc component was sensitive to glibenclamide but not to DIDS, suggesting that a cystic fibrosis transmembrane conductance regulator (Cftr)-mediated anion conductance was responsible. Basal Cl--dependent HCO3- secretion, measured using a pH stat technique, was decreased significantly in anti-CD3-injected mice, with a simultaneous increase in Cl--independent HCO3- secretion that was also inhibited by glibenclamide. Experiments using Cftr-/- mice showed neither an increase in Isc nor an increase in HCO3- secretion, confirming the role for Cftr protein in stimulating anion secretion following anti-CD3 treatment. Western blot analysis indicated that Cftr protein levels were unaltered by anti-CD3 treatment, at least acutely. Finally, an immunoassay for cAMP showed significant increases in intracellular cAMP in villus cells, but not in crypt cells. These studies therefore suggest a shift from a predominantly electroneutral Cl-HCO3- exchange in normal mice, to a predominantly electrogenic anion secretion including HCO3- that occurs via functional Cftr during anti-CD3-mediated acute inflammation.

Butyrate induces intestinal sodium absorption via Sp3-mediated transcriptional up-regulation of epithelial sodium channels

BACKGROUND & AIMS

The epithelial sodium channel (ENaC) is the rate-limiting factor for colonic electrogenic sodium absorption. This study aimed to investigate ENaC regulation by butyrate, a short-chain fatty acid (SCFA) produced by intestinal bacteria.

METHODS

ENaC was examined in HT-29/B6 cells and glucocorticoid receptor(GR)-transfected HT-29/B6 cells (HT-29/B6-GR) by reverse-transcription polymerase chain reaction, real-time polymerase chain reaction, and confocal microscopy. ENaC promoters were investigated by deletion/mutation analysis, electrophoretic mobility shift assays, and quantitative chromatin immunoprecipitation. Sodium transport of HT-29/B6-GR cells and rat distal colon was quantified in Ussing chambers.

RESULTS

Butyrate up-regulated beta- and gamma-ENaC mRNA expression in HT-29/B6 cells and induced transcription from beta- and gamma-ENaC promoter constructs. The gamma-ENaC promoter could also be induced by the SCFA propionate but not by acetate. Deletion/mutation assays revealed that activation of the gamma-ENaC promoter depended on 2 GC boxes, which were shown to bind Sp1 and Sp3 in vitro. Although both transcription factors increased butyrate-mediated gamma-ENaC transcription upon overexpression, chromatin immunoprecipitation revealed that only Sp3 binds to the gamma-ENaC promoter in vivo and that Sp3 binding is enhanced by butyrate. Transcriptional ENaC induction by butyrate led to synthesis of gamma-ENaC subunits, but correct targeting of ENaC channels to the apical cell membrane was dependent on corticosteroid hormones. Finally, butyrate substantially increased electrogenic sodium absorption via ENaC in the presence of corticosteroid hormones in HT-29/B6-GR cells and in rat distal colon.

CONCLUSIONS

Concerted action of SCFA and corticosteroid hormones is required for induction of ENaC and maintenance of intestinal electrogenic sodium absorption.

Evaluation of oral rehydration solution by whole-gut perfusion in rats: effect of osmolarity, sodium concentration and resistant starch

BACKGROUND

Reduced osmolarity oral rehydration solution (ORS) improved small bowel absorption of fluid and electrolytes in segmental perfusion in experimental animals; this was borne out in clinical practice. Adding amylase-resistant starch (RS) to ORS is expected to increase colonic fluid absorption. This study used combined small and large bowel perfusion to evaluate combinations of reduced osmolarity and starch in ORS.

METHODS

Single-pass steady-state perfusions of the whole gut at 30 mL/h, using the nonabsorbable marker C-polyethylene glycol 4000, were performed in Wistar rats after exposure to cholera toxin or Escherichia coli heat-stable enterotoxin (STa).

RESULTS

Steady state was established within 90 minutes after commencing perfusion. Net secretion of water, sodium and chloride induced by cholera toxin was partially reversed by standard glucose-ORS (G-ORS). Substituting glucose in G-ORS with RS (RS-ORS) substantially increased net water absorption (P < 0.001) as did reduced osmolarity ORS (RO-ORS) (P < 0.001); addition of RS to RO-ORS further increased water absorption (P < 0.001). In STa-treated intestine, RO-ORS and RS-ORS significantly improved water absorption compared to G-ORS (P < 0.005). RO- and RS-RO-ORS did not significantly augment net electrolyte absorption compared with G-ORS. RS-ORS was associated with highest net absorption of sodium and chloride compared with all other groups.

CONCLUSIONS

RS increased net water (and sodium) absorption from isosmolar and reduced osmolar ORS consistent with increased absorption by the colon. RS in reduced osmolar ORS may have advantages to reduce severity of diarrhea and prevent hyponatremia in severe diarrhea and may be applicable to diarrhea of different etiologies.

Amylase-resistant starch as adjunct to oral rehydration therapy in children with diarrhea

BACKGROUND

Oral rehydration solution (ORS) for treatment of diarrhea relies on enhancement of small intestinal sodium and fluid absorption to correct dehydration. Amylase-resistant starch added to ORS significantly reduced the duration and severity of diarrhea in adults with cholera, presumably by generation of short-chain fatty acids in the colon and enhancement of colonic sodium and fluid absorption. The present study was initiated to determine whether addition of amylase-resistant starch to standard World Health Organization glucose-ORS (G-ORS) would reduce the duration of diarrhea and fecal fluid losses in children with acute diarrhea.

METHODS

One hundred eighty-three children (6 months to 3 years) with acute watery diarrhea were randomized to receive either standard treatment with G-ORS or G-ORS with additional amylase-resistant starch, HAMS (HAMS-ORS, 50g/L). Stool weight and consistency were monitored serially until development of formed stool or development of treatment failure defined as either the need for unscheduled intravenous fluid therapy or diarrhea longer than 72 hours.

RESULTS

Five of the subjects were lost to follow up. In 178 remaining children (87 HAMS-ORS and 91 G-ORS) with evaluable data, time from enrolment to last unformed stool was significantly less in children receiving HAMS-ORS (median, 6.75 hours; 95% confidence interval, 4.27-9.22) than in children treated with G-ORS (12.80 hours, 8.69-16.91) (P = 0.0292). Time to first formed stool was also significantly shorter in children receiving HAMS-ORS (median, 18.25 hours; 95% confidence interval, 13.09-23.41) compared with children receiving G-ORS (median, 21.50 hours; 95% confidence interval, 17.26-25.74) (P = 0.0440). The total amount of ORS consumed was similar in both groups. There was a trend toward lower mean stool weight in first 24 hours (P = 0.0752) as well as total diarrheal stool weight (P = 0.0926) in patients in the HAMS group compared with the G-ORS group.

CONCLUSION

In children with acute diarrhea, the addition of amylase-resistant starch to glucose ORS significantly shortened duration of diarrhea compared with standard treatment.

The chemopreventive agent resveratrol stimulates cyclic AMP-dependent chloride secretion in vitro

Resveratrol and its analogs are promising cancer chemoprevention agents, currently under investigation in clinical trials. However, patients administered other plant polyphenols experienced severe diarrhea, likely due to an increase in intracellular cyclic AMP (cAMP). Resveratrol itself raises intracellular cAMP levels in breast cancer cells in vitro. Its future use as a cancer chemopreventive agent could therefore be compromised by its severe side effects. The aim of the study was (a) to define the influence of resveratrol on intestinal Cl(-) secretion and (b) to elucidate possible intracellular transduction pathways involved. Resveratrol caused a dose- and time-dependent increase in DeltaIsc in T(84) cells. The specificity of resveratrol was confirmed by using piceatannol 100 mumol/L, the hydroxylated resveratrol analog, which did not alter DeltaIsc. A significant elevation of [cAMP](i) by resveratrol was assessed in T(84) cells. In mouse jejunum, resveratrol induced a time- and dose-dependent increase in DeltaIsc as well. In bilateral Cl(-)-free medium, as well as after inhibition of protein kinase A, resveratrol-induced DeltaIsc was reduced significantly. Preincubation of T(84) cells with butyrate 2 mmol/L (24 and 48 hours) significantly inhibited resveratrol as well as forskolin-induced Cl(-) secretion. In summary, the main mechanism of action of resveratrol in intestinal epithelia is cAMP-induced chloride secretion which can be suppressed by butyrate. It can therefore be suggested that in cancer chemoprevention, both agents should be combined to reduce an undesired side effect such as diarrhea and to benefit from the known agonistic effect of both agents on differentiation of colon cancer cells.

Thiazide-sensitive NaCl-cotransporter in the Intestine

Thiazides, such as hydrochlorothiazide (HCTZ), are used to control blood pressure and to reduce renal calcium excretion. These effects are a result of interactions with the NaCl-cotransporter (NCC). This is demonstrated by the fact that mutations within the NCC protein lead to salt-resistant hypotension and hypocalciuria, paralleled by an increase in bone mineral density. These symptoms are also known as Gitelman syndrome. It has become increasingly evident that the effect of HCTZ on blood pressure and calcium homeostasis cannot be attributed exclusively to kidney functions, where the primary action of HCTZ on NCC is postulated to occur. We demonstrated the presence of the NCC transporter in the rat small intestine (ileum and jejunum) and human HT-29 cells, by using reverse transcription-PCR, Northern blot, Western blot, and immunofluorescence. Furthermore, we show that HCTZ modulates Ca(2+) uptake by intestinal cells, while affecting the electrical parameters of the cellular membrane, thus suggesting a functional interaction between NCC and the epithelial voltage-dependent calcium channel. The experiments presented here support the hypothesis of a direct involvement of the intestinal cells in the interaction between HCTZ and NaCl, as well as calcium homeostasis.

Comparison of two Chinese medical herbs, Huangbai and Qianniuzi, on influence of short circuit current across the rat intestinal epithelia

Huangbai (Phellodendron spec.) and Qianniuzi (Pharbitis spec.) are two traditional Chinese medical herbs used for anti-diarrheal and laxative agents, respectively. Ethanol and water extracts of these two herbs were prepared and effects of the extracts on ion transport of the rat intestinal epithelia were studied. For measuring changes of the short circuit current across the epithelia, the rat intestinal epithelia were mounted in the Ussing chamber and attached with voltage/current clamp. The intestinal epithelia were firstly activated by serosal administration of 5 microM forskolin. As current raised and being stable, extracts of these herbs were added, respectively, and changes in the short circuit current were recorded. Ethanol extract of Huangbai attenuated the current increment; on the contrary, ethanol extract of Qianniuzi augmented the current increment additionally. Water extracts of the two herbs showed minor effects on the current in comparison to ethanol extracts. The results provide evidences to reveal the pharmacological mechanism of the two Chinese medical herbs on the intestinal tissue.

Trophic and cytoprotective nutrition for intestinal adaptation, mucosal repair, and barrier function

Intestinal epithelial cell turnover (proliferation, migration, differentiation, and apoptosis) and gut barrier functions are dynamic processes that are markedly affected by nutritional status, the route of feeding, and the adequacy of specific nutrients in the diet. Emerging studies are defining potential therapeutic roles for specific nutrients and diet-derived compounds (including arginine, glutamate, glutamine, glutathione, glycine, vitamin A, zinc, and specific lipids) in gut mucosal turnover, repair, adaptation after massive bowel resection, and barrier function. The role and regulation of endogenous bowel flora in generating short-chain fatty acids from diet-derived fiber and other diet-derived compounds and the effects of these agents on gut function are increasingly being elucidated. Results of these investigations should define new nutritional methods for trophic and cytoprotective effects on the intestine in conditions such as inflammatory bowel disease, malnutrition, and short bowel syndrome.