Review article: Small intestinal bacterial overgrowth, bile acid malabsorption and gluten intolerance as possible causes of chronic watery diarrhoea.

BACKGROUND: Chronic watery diarrhoea is one of the most common symptoms prompting GI evaluation. Recently, new diagnostic considerations have emerged as possible factors in chronic diarrhoea. AIM: To review available data regarding diagnosis and treatment of chronic diarrhoea with an emphasis on bacterial overgrowth and bile acid malabsorption. METHODS: A systematic search of the English language literature of chronic diarrhoea was performed focused on three possible aetiologies of diarrhoea: small intestinal bacterial overgrowth (SIBO), idiopathic bile salt malabsorption (IBAM), gluten responsive enteropathy. RESULTS: Recent studies suggest that SIBO and bile acid malabsorption may have been underestimated as possible causes of chronic watery diarrhoea. Gluten intolerance with negative coeliac serology is a contentious possible cause of watery diarrhoea, but requires further research before acceptance as an entity. CONCLUSION: In patients with otherwise unexplained chronic watery diarrhoea, small intestinal bacterial overgrowth and bile salt malabsorption should be considered and investigated.

Dietary pectin and calcium inhibit colonic proliferation in vivo by differing mechanisms.

Diet plays an important role in promoting and/or preventing colon cancer; however, the effects of specific nutrients remain uncertain because of the difficulties in correlating epidemiological and basic observations. Transmissible murine colonic hyperplasia (TMCH) induced by Citrobacter rodentium, causes significant hyperproliferation and hyperplasia in the mouse distal colon and increases the risk of subsequent neoplasia. We have recently shown that TMCH is associated with an increased abundance of cellular beta-catenin and its nuclear translocation coupled with up-regulation of its downstream targets, c-myc and cyclin D1. In this study, we examined the effects of two putatively protective nutrients, calcium and soluble fibre pectin, on molecular events linked to proliferation in the colonic epithelium during TMCH. Dietary intervention incorporating changes in calcium [high (1.0%) and low (0.1%)] and alterations in fibre content (6% pectin and fibre-free) were compared with the standard AIN-93 diet (0.5% calcium, 5% cellulose), followed by histomorphometry and immunochemical assessment of potential oncogenes. Dietary interventions did not alter the time course of Citrobacter infection. Both 1.0% calcium and 6% pectin diet inhibited increases in proliferation and crypt length typically seen in TMCH. Neither the low calcium nor fibre-free diets had significant effect. Pectin diet blocked increases in cellular beta-catenin, cyclin D1 and c-myc levels associated with TMCH by 70%, whereas neither high nor low calcium diet had significant effect on these molecules. Diets supplemented with either calcium or pectin therefore, exert anti-proliferative effects in mouse distal colon involving different molecular pathways. TMCH is thus a diet-sensitive model for examining the effect of specific nutrients on molecular characteristics of the pre-neoplastic colonic epithelium.

Patient evaluation and management with selective use of magnetic resonance cholangiography and endoscopic retrograde cholangiopancreatography before laparoscopic cholecystectomy.

OBJECTIVE: To assess the utility of triage guidelines for patients with cholelithiasis and suspected choledocholithiasis, incorporating selective use of magnetic resonance cholangiography (MRC) and endoscopic retrograde cholangiopancreatography (ERCP) before laparoscopic cholecystectomy (LC). SUMMARY BACKGROUND DATA: ERCP is the most frequently used modality for the diagnosis and resolution of choledocholithiasis before LC. MRC has recently emerged as an accurate, noninvasive modality for the detection of choledocholithiasis. However, useful strategies for implementing this diagnostic modality for patient evaluation before LC have not been investigated. METHODS: During a 16-month period, the authors prospectively evaluated all patients before LC using triage guidelines incorporating patient information obtained from clinical evaluation, serum chemistry analysis, and abdominal ultrasonography. Patients were then assigned to one of four groups based on the level of suspicion for choledocholithiasis (group I, extremely high; group 2, high; group 3, moderate; group 4, low). Group 1 patients underwent ERCP and clearance of common bile duct stones; group 2 patients underwent MRC; group 3 patients underwent LC with intraoperative cholangiography; and group 4 patients underwent LC without intraoperative cholangiography. RESULTS: Choledocholithiasis was detected in 43 of 440 patients (9.8%). The occurrence of choledocholithiasis among patients in the four groups were 92.6% (25/27), 32.4% (12/37), 3.8% (2/52), and 0.9% (3/324) for groups 1, 2, 3, and 4, respectively (P <.001). MRC was used for 8.4% (37/440) of patients. Patient triage resulted in the identification of common bile duct stones during preoperative ERCP in 92.3% (36/39) of the patients. Unsuspected common bile duct stones occurred in six patients (1.4%). CONCLUSIONS: The probability of choledocholithiasis can be accurately assessed based on information obtained during the initial noninvasive evaluation. Stratification of risks for choledocholithiasis facilitates patient management with the most appropriate diagnostic studies and interventions, thereby improving patient care and resource utilization.

Increased beta-catenin expression and nuclear translocation accompany cellular hyperproliferation in vivo.

Beta-catenin performs critical roles in development and cellular adhesion. More recently, an oncogenic role has been described. In colon cancer, decreased E-cadherin/beta-catenin association is causally linked to increased beta-catenin-regulated gene expression and increased cellular division. Whether the same pathway is active in native epithelia remains unknown. To address this question, we used the transmissible murine colonic hyperplasia model to measure changes in beta-catenin abundance, nuclear partitioning, target gene (c-myc and cyclin D1) expression, and subcellular distribution. Colonocyte hyperproliferation was associated with a 4.3 +/- 0.56 (SD)-fold increase in total cellular beta-catenin protein content, whereas modest changes in gamma-catenin and E-cadherin expression were recorded. The beta-catenin signal increased before changes in mucosal crypt length, a gross index of cellular proliferation/apoptosis. Beta-catenin detected in Triton X-100-soluble (cytosolic) cellular fractions was enriched 4.3 +/- 0.9 (SD)-fold, whereas a modest decrease of 0.9 +/- 0.09 (SD)-fold was recorded in Triton X-100-insoluble (cytoskeletal) fractions. After these changes, nuclear beta-catenin partitioning increased 2.4 +/- 0.4 (SD)-fold, accompanied by 2.5 +/- 0.4- and 4.0 +/- 0.8-fold (SD) increases in cellular c-myc and cyclin D1 levels, respectively. Thus, increased cellular cytosolic and nuclear beta-catenin levels were associated with increased beta-catenin target protein expression. Significant alterations in beta-catenin subcellular distribution were also recorded immunohistochemically. Apical/lateral junctional labeling was observed in normal crypts with increased lateral membrane staining within the upper regions. During transmissible murine colonic hyperplasia, these gradients were dissipated, and basilar plaques were formed within a subset of basal crypt cells. These findings predict that an oncogenic signaling mechanism related to non-E-cadherin-bound beta-catenin is active in hyperproliferating native colonocytes and is similar to that recorded during the early stages of colon carcinogenesis.

SCFA increase intestinal Na absorption by induction of NHE3 in rat colon and human intestinal C2/bbe cells.

Short-chain fatty acids (SCFA), produced by colonic bacterial flora fermentation of dietary carbohydrates, promote colonic Na absorption through mechanisms not well understood. We hypothesized that SCFA promote increased expression of apical membrane Na/H exchange (NHE), serving as luminal physiological cues for regulating colonic Na absorptive capacity. Studies were performed in human colonic C2/bbe (C2) monolayers and in vivo. In C2 cells exposed to butyrate, acetate, proprionate, or the poorly metabolized SCFA isobutyrate, apical membrane NHE3 activity and protein expression increased in a time- and concentration-dependent manner, whereas no changes were observed for NHE2. In contrast, no significant changes in brush-border hydrolase or villin expression were noted. Analogous to the in vitro findings, rats fed the soluble fiber pectin exhibited a time-dependent increase in colonic NHE3, but not NHE2, protein, mRNA, and brush-border activity. These changes were region-specific, as no changes were observed in the ileum. We conclude that luminal SCFA are important physiological cues for regulating colonic Na absorptive function, allowing the colon to adapt to chronic changes in dietary carbohydrate and Na loads.

The pathophysiology of diarrhea.

Diarrhea is a very common event after transplantation, but its cause may be difficult to identify. The first step in determining the cause in any particular case is an understanding of the etiology of diarrhea in general. Although diarrhea often is categorized into such types as secretory versus osmotic, or electrolyte transport-related versus motility-related, a thorough understanding of the problem requires knowledge of how the paracrine, immune, nervous and endocrine systems react to each other as well as to infection, drugs or other stimuli.

Increased nuclear translocation of catalytically active PKC-zeta during mouse colonocyte hyperproliferation.

Protein kinase (PK) C-zeta is implicated in the control of colonic epithelial cell proliferation in vitro. However, less is known about its physiological role in vivo. Using the transmissible murine colonic hyperplasia (TMCH) model, we determined its expression, subcellular localization, and kinase activity during native crypt hyperproliferation. Enhanced mitosis was associated with increased cellular 72-kDa holoenzyme (PKC-zeta, 3.2-fold), 48-kDa catalytic subunit (PKM-zeta, 3- to 9-fold), and 24-kDa membrane-bound fragment (M(f)-zeta, >10-fold) expression. Both PKC-zeta and PKM-zeta exhibited intrinsic kinase activity, and substrate phosphorylation increased 4.5-fold. No change in cellular PKC-iota/PKM-iota expression occurred. The subcellular distribution of immunoreactive PKC-zeta changed significantly: neck cells lost their basal subcellular pole filamentous staining, whereas proliferating cell nuclear antigen-positive cells exhibited elevated cytoplasmic, lateral membrane, and nuclear staining. Subcellular fractionation revealed increased PKC-zeta and PKM-zeta expression and activity within nuclei, which preferentially accumulated PKM-zeta. These results suggest separate cellular and nuclear roles, respectively, for PKC-zeta in quiescent and mitotically active colonocytes. PKM-zeta may specifically act as a modulator of proliferation during TMCH.

Murine colonic mucosa hyperproliferation. I. Elevated CFTR expression and enhanced cAMP-dependent Cl(-) secretion.

Fluid transport in the large intestine is mediated by the cystic fibrosis gene product and cAMP-dependent anion channel cystic fibrosis transmembrane conductance regulator (CFTR). cAMP-mediated Cl(-) secretion by gastrointestinal cell lines in vitro has been positively correlated with the insertion of CFTR into the apical membrane of differentiated senescent colonocytes and negatively correlated with the failure of CFTR to insert into the plasma membrane of their undifferentiated proliferating counterparts. In native tissues, this relationship remains unresolved. We demonstrate, in a transmissible murine colonic hyperplasia (TMCH) model, that (8-fold) colonocyte proliferation was accompanied by increased cellular CFTR mRNA and protein expression (8.3- and 2.4-fold, respectively) and enhanced mucosal cAMP-dependent Cl(-) secretion (2. 3-fold). By immunofluorescence microscopy, cellular CFTR expression was restricted to the apical pole of cells at the base of the epithelial crypt. In contrast, increased cellular proliferation in vivo led to increases in both the cellular level and the total number of cells expressing this anion channel, with cellular CFTR staining extending into the crypt neck region. Hyperproliferating colonocytes accumulated large amounts of CFTR in apically oriented subcellular perinuclear compartments. This novel mode of CFTR regulation may explain why high endogenous levels of cellular CFTR mRNA and protein within the TMCH epithelium were not matched with larger increases in transmucosal CFTR Cl(-) current.

Murine colonic mucosa hyperproliferation. II. PKC-beta activation and cPKC-mediated cellular CFTR overexpression.

In the companion article (Umar S, Scott J, Sellin JH, Dubinsky WP, and Morris AP, Am J Physiol Gastrointest Liver Physiol 278: 753-764, 2000), we have shown that transmissible murine colonic hyperplasia (TMCH) increased cellular cystic fibrosis transmembrane conductance regulator (CFTR) mRNA and protein expression, relocalized CFTR within colonocytes, and enhanced mucosal cAMP-dependent Cl(-) secretion. We show here that these changes were dependent on elevated cellular levels of membrane-bound Ca(2+)- and diacylglycerol-sensitive protein kinase C (PKC) activity (12-fold), induced by selective (3- to 4-fold) rises in conventional PKC (cPKC) isoform expression and membrane translocation. Three cPKC isoforms were detected in isolated crypts: alpha, beta1, and beta2. cPKC-beta1 rises preceded and those of cPKC-alpha and cPKC-beta2 paralleled cellular hyperproliferation and its effects on CFTR expression and cAMP-dependent Cl(-) current secretion. Only cPKC-beta1 and cPKC-beta2 were membrane translocated during TMCH. Furthermore, only cPKC-beta1 trafficked to the nucleus, whereas cPKC-beta2 remained partitioned among cytosolic, membrane, and cytoskeletal subcellular fractions. Modest increases in novel PKC-epsilon (nPKC-epsilon) expression and subcellular membrane partitioning were recorded during TMCH, but no changes were seen for PKC-delta or -eta. No nPKC isoform nuclear partitioning was detected. The orally bioactive cPKC inhibitor Ro-32-0432 reversed both TMCH and elevated cellular CFTR mRNA levels, whereas a pharmacologically inert analog (Ro-31-6045) failed to inhibit either response. On the basis of these facts, we present a new hypothesis whereby PKC-dependent cellular proliferation promotes endogenous cellular CFTR levels. PKC-beta1 was identified as a candidate regulatory PKC isoform.

Effect of increased fluid intake on stool output in normal healthy volunteers.

Constipation is a common condition affecting millions of people throughout the world. The present study aimed to determine the effect of extra fluid intake, as recommended by many primary care physicians and gastroenterologists, on the actual stool output in normal healthy volunteers. We recruited 15 healthy volunteers (aged 23-46 years, mean 30.1) without any significant history of diarrhea or constipation to participate in our study. Nine subjects underwent extra intake of isotonic fluids (Gatorade), whereas the remainder received extra free water over their baseline. During period I (3 days), baseline diet and fluid intake were determined by a registered dietitian. During periods II and III (2 days each), the volunteers in each group increased their fluid intake by 1 and 2 l of isotonic (Gatorade) and hypotonic solution (water), respectively. Period IV (2 days) completed the study with the volunteers returning to their baseline fluid intake. Urine and stool outputs were measured in these volunteers. Additional increase in fluid intake (isotonic or free water) did not result in a significant change in stool output. However, there was a significant increase in urine output (P < 0.05). Despite common medical advice to consume extra fluid for constipation, our results indicate that extra fluid intake in normal healthy volunteers did not produce a significant increase in stool output.

Review article: short chain fatty acids in health and disease.

Short chain fatty acids (SCFAs) have been the subject of much research over the past few decades. They play a vital role in maintenance of colonic integrity and metabolism. They are produced when dietary fibre is fermented by colonic bacteria. SCFAs are avidly absorbed in the colon, at the same time as sodium and water absorption and bicarbonate secretion. Once absorbed, SCFAs are used preferentially as fuel for colonic epithelial cells and have trophic effects on the epithelium. Clinically, SCFAs have been studied as possible therapeutic agents in diversion colitis, ulcerative colitis, radiation proctitis, pouchitis and antibiotic-associated diarrhoea. Although some promising effects have been observed in uncontrolled studies, a specific therapeutic role for SCFAs remains to be defined. SCFAs may be the effector of the beneficial role of fibre in prevention of colon cancer.

Short-chain fatty acids have polarized effects on sodium transport and intracellular pH in rabbit proximal colon.

BACKGROUND & AIMS: Short-chain fatty acids (SCFAs) stimulate colonic Na+ absorption, presumably by acidification of colonocytes and activation of apical Na+/H+ exchangers. It is unclear whether this effect depends on SCFA gradients across the colonic epithelium, and, if so, why. The aim of this study was to determine (1) whether SCFAs added unilaterally to either the apical or basolateral border of the cell have similar effects on intracellular pH (pHi); (2) whether SCFA gradients alter Na+ transport and; (3) what regulatory factors are involved in gradient-induced Na+ transport. METHODS: pHi was measured in intact epithelial rabbit proximal colon using the pH-sensitive indicator 2',7'-bis(carboxyethyl)-5-(6)-carboxyfluorescein, and Na+ transport was measured under short-circuit conditions. RESULTS: Apical and basolateral SCFAs had equivalent effects on decreasing pHi, but the recovery toward baseline was more vigorous after apical SCFAs. Gradients of both propionate and lactate (50 mmol/L [mucosal], 0 mmol/L [serosal]) stimulated electroneutral Na+ absorption, which was inhibited by bicarbonate, mucosal 4,4'-diisothiocyanostilbene-2, 2'-disulfonic acid, and Cl- removal. However, it was not blocked by amiloride. The differential response to a series of pharmacological agents showed that gradient-stimulated transport is distinct from epinephrine-stimulated electroneutral Na+ absorption. CONCLUSIONS: A physiological gradient of SCFAs across the colonic epithelium elicits polarized effects on both pHi and Na+ absorption that may be important determinants of colonic fluid transport.

Short chain fatty acid rectal irrigation for left-sided ulcerative colitis: a randomised, placebo controlled trial.

BACKGROUND: Short chain fatty acid (SCFA) deficiency is associated with colitis in animals and humans, and the mucosal metabolism of these compounds is decreased in ulcerative colitis. AIMS: To assess the efficacy of topical SCFA treatment in ulcerative colitis. PATIENTS AND METHODS: 103 patients with distal ulcerative colitis were entered into a six week, double-blind, placebo controlled trial of rectal SCFA twice daily; patients who were unchanged on placebo were offered SCFA in an open-label extension trial. RESULTS: Of the 91 patients completing the trial, more patients in the SCFA treated than in the placebo treated group improved (33% v 20%, p = 0.14, NS). Those on SCFA also had larger, but statistically non-significant, reductions in every component of their clinical and histological activity scores. In patients with a relatively short current episode of colitis (< 6 months, n = 42), more responded to SCFA than to placebo (48% v 18%, p = 0.03). These patients also had larger, but statistically non-significant, decreases in their clinical activity index (p = 0.08 v placebo). Every patient who improved used at least five of six of the prescribed rectal SCFA irrigations, whereas only 37% who did not improve were as compliant. In the open-label extension trial, 65% improved on SCFA; these patients also had significant reductions (p < 0.02) in their clinical and histological activity scores. CONCLUSIONS: Although SCFA enemas were not of therapeutic value in this controlled trial, the results suggest efficacy in subsets of patients with distal ulcerative colitis including those with short active episodes. Prolonged contact with rectal mucosa seems to be necessary for therapeutic benefit.

Differing mechanisms of stimulation of Na+ absorption in rabbit proximal colon.

Both alpha2-adrenergic agonists and decreased Na+ in the bathing fluids stimulate electroneutral Na+ absorption in rabbit proximal colon, but it is unclear whether they have similar modes of action. We sought to define regulatory events involved with stimulation of Na+ absorption by these two agonists. Transport parameters were assessed by ion flux studies under short-circuit and pH stat conditions, recordings of intracellular electrical potential difference (psi(mc)) with microelectrode impalements, and measurement of intracellular pH (pH(i)). Epinephrine elicited a yohimbine-inhibitable alkalinization of pH(i) but did not alter psi(mc) In contrast, lowered serosal Na+ concentration ([Na+]) did not significantly increase pH(i) but did depolarize psi(mc). Removal of serosal HCO(3)- stimulated Na+ absorption and reversed residual ion flux from secretion to absorption. pH stat studies demonstrated epinephrine-stimulated, amiloride-inhibitable serosal alkalinization. Serosal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid inhibited Na+ absorption. Epinephrine and lowered [Na+] have different effects on intracellular parameters associated with electroneutral Na+ absorption. Epinephrine stimulates an apical Na+/H+ exchanger. Lowered [Na+] elicits responses consistent with a coupled Na+-HCO(3x)- exit step. Coordinated function of apical Na+/H+ exchangers and a basolateral Na+-HCO(3)(x)- symport permit Cl(-)-independent electroneutral Na+ absorption while maintaining pH(i) homeostasis. Given the low [Cl-] environment of the colonic lumen, this transport pathway may be important for electroneutral Na+ absorption.