[Position paper on reporting of intestinal ultrasound findings in patients with inflammatory bowel disease]. / Positionspapier zur Befunderhebung von Darmultraschallbefunden bei chronisch entzündlichen Darmerkrankungen.

BACKGROUND: Intestinal ultrasound is increasingly used for primary diagnosis, detection of complications and monitoring of patients with Crohn's disease and ulcerative colitis. Standardization of reporting is relevant to ensure quality of the methodology and to improve communication between different specialties. The current manuscript describes the features required for optimized reporting of intestinal ultrasound findings in inflammatory bowel disease (IBD). METHODS: An expert consensus panel of gastroenterologists, radiologists, pathologists, paediatric gastroenterologists and surgeons conducted a systematic literature search. In a Delphi- process members of the Kompetenznetz Darmerkrankungen in collaboration with members of the German Society for Radiology (DRG) voted on relevant criteria for reporting of findings in intestinal ultrasound. Based on the voting results statements were agreed by expert consensus. RESULTS: Clinically relevant aspects of intestinal ultrasound (IUS) findings have been defined to optimize reporting and to standardize terminology. Minimal requirements for standardized reporting are suggested. The statements focus on description of disease activity as well as on complications of IBD. Attributes of intestinal inflammation are described and illustrated by exemplary images. CONCLUSION: The current manuscript provides practical recommendations on how to standardize documentation and reporting from intestinal ultrasound findings in patients with IBD.

Microbiota-associated Risk Factors for Clostridioides difficile Acquisition in Hospitalized Patients: A Prospective, Multicentric Study.

BACKGROUND: Asymptomatic C. difficile colonization is believed to predispose to subsequent C. difficile infection (CDI). While emerging insights into the role of the commensal microbiota in mediating colonization resistance against C. difficile have associated CDI with specific microbial components, corresponding prospectively collected data on colonization with C. difficile are largely unavailable. METHODS: C. difficile status was assessed by GDH EIA and real-time PCR targeting the toxin A (tcdA) and B (tcdB) genes. 16S V3 and V4 gene sequencing results from fecal samples of patients tested positive for C. difficile were analyzed by assessing alpha and beta diversity, LefSe, and the Piphillin functional inference approach to estimate functional capacity. RESULTS: 1506 patients were recruited into a prospective observational study (DRKS00005335) upon admission into one of five academic hospitals. 936 of them provided fecal samples on admission and at discharge and were thus available for longitudinal analysis. Upon hospital admission, 5.5% (83/1506) and 3.7% (56/1506) of patients were colonized with toxigenic (TCD) and non-toxigenic C. difficile (NTCD), respectively. During hospitalization, 1.7% (16/936) acquired TCD. Risk factors for acquisition of TCD included pre-existing lung diseases, lower GI endoscopy and antibiotics. Species protecting against hospital-related C. difficile acquisition included Gemmiger spp., Odoribacter splanchnicus, Ruminococcus bromii and other Ruminococcus spp. Metagenomic pathway analysis identified steroid biosynthesis as the most underrepresented metabolic pathway in patients who later acquire C. difficile colonization. CONCLUSIONS: Gemmiger spp., Odoribacter splanchnicus, Ruminococcus bromii and other Ruminococci were associated with a decreased risk of C. difficile acquisition. CLINICAL TRIALS REGISTRATION: DRKS00005335.

[Position paper on endoscopic reporting in IBD]. / Positionspapier zur Befunderstellung endoskopischer Untersuchungen bei Patienten mit chronisch-entzündlichen Darmerkrankungen.

The complete and reliable documentation of endoscopic findings make up the crucial foundation for the treatment of patients with inflammatory bowel diseases such as Crohn´s disease and ulcerative colitis. These findings are, on the one hand, a prerequisite for therapeutic decisions and, on the other hand, important as a tool for assessing the response to ongoing treatments. Endoscopic reports should, therefore, be recorded according to standardized criteria to ensure that the findings of different endoscopists can be adequately compared and that changes in the course of the disease can be traced back. In consideration of these necessities, fifteen members of the Imaging Working Group of the German Kompetenznetz Darmerkrankungen have created a position paper proposing a structure and specifications for the documentation of endoscopic exams. In addition to the formal report structure, the recommendations address a large number of attributes of acute and chronic inflammatory alterations as well as endoscopically detectable complications, which are explained in detail and illustrated using exemplary images. In addition, more frequently used endoscopic activity indices are presented and their use in everyday clinical practice is discussed.

Evidence for a causal link between adaptor protein PDZK1 downregulation and Na⁺/H⁺ exchanger NHE3 dysfunction in human and murine colitis.

A dysfunction of the Na(+)/H(+) exchanger isoform 3 (NHE3) significantly contributes to the reduced salt absorptive capacity of the inflamed intestine. We previously reported a strong decrease in the NHERF family member PDZK1 (NHERF3), which binds to NHE3 and regulates its function in a mouse model of colitis. The present study investigates whether a causal relationship exists between the decreased PDZK1 expression and the NHE3 dysfunction in human and murine intestinal inflammation. Biopsies from the colon of patients with ulcerative colitis, murine inflamed ileal and colonic mucosa, NHE3-transfected Caco-2BBe colonic cells with short hairpin RNA (shRNA) knockdown of PDZK1, and Pdzk1-gene-deleted mice were studied. PDZK1 mRNA and protein expression was strongly decreased in inflamed human and murine intestinal tissue as compared to inactive disease or control tissue, whereas that of NHE3 or NHERF1 was not. Inflamed human and murine intestinal tissues displayed correct brush border localization of NHE3 but reduced acid-activated NHE3 transport activity. A similar NHE3 transport defect was observed when PDZK1 protein content was decreased by shRNA knockdown in Caco-2BBe cells or when enterocyte PDZK1 protein content was decreased to similar levels as found in inflamed mucosa by heterozygote breeding of Pdzk1-gene-deleted and WT mice. We conclude that a decrease in PDZK1 expression, whether induced by inflammation, shRNA-mediated knockdown, or heterozygous breeding, is associated with a decreased NHE3 transport rate in human and murine enterocytes. We therefore hypothesize that inflammation-induced loss of PDZK1 expression may contribute to the NHE3 dysfunction observed in the inflamed intestine.

Patients with Inflammatory Bowel Disease Show Fewer Sex-Related Differences in Their Dietary Behavior Than the General Population: A Qualitative Analysis.

BACKGROUND: Since diet is generally recognized as an important factor directly modulating the gut microbiome, it is also considered a potential environmental triggering factor for the pathogenesis and onset of inflammatory bowel disease (IBD). While the habitual and sex-related dietary behavior of the general population has been the subject of extensive study and reporting, data on IBD patients' dietary behavior and especially its sex-related differences are underrepresented. However, as diet is an important factor in the course of IBD, we hypothesized that men and women with IBD have a different dietary profile than the general population. METHODS: We performed a cohort analysis of a monocentric, cross-sectional study and compared the sex-related dietary behavior of 82 IBD patients (n = 40 women) to a sex- and age-matched cohort of the general German population [n = 328 (n = 160 women)]. Further on, disease-related quality of life and fecal calprotectin were correlated to the IBD patients' dietary behavior. RESULTS: While sex-related dietary behavior was frequently of statistical difference in the general population within the IBD cohort, only minor numerical differences were observed between the sexes, which were rarely statistically significant. However, correlation analyses of disease-related quality of life (IBDQ) and diet revealed significant differences in male IBD patients but not in female IBD patients (p = 0.007; r = 0.409 for energy intake (kJ/d); p = 0.003, r = 0.449 for adherence to Mediterranean diet). CONCLUSION: The dietary behavior of IBD patients showed more similarity between the sexes than the general German population. Distinct sex-related trends and differences in correlation with disease parameters demonstrated a significant difference for an adaptive dietary behavior, especially in IBD men.

Essential role of the electroneutral Na+-HCO3- cotransporter NBCn1 in murine duodenal acid-base balance and colonic mucus layer build-up in vivo.

Duodenal epithelial cells need efficient defence strategies during gastric acidification of the lumen, while colonic mucosa counteracts damage by pathogens by building up a bacteria-free adherent mucus layer. Transport of HCO3(-) is considered crucial for duodenal defence against acid as well as for mucus release and expansion, but the transport pathways involved are incompletely understood. This study investigated the significance of the electroneutral Na(+)-HCO3(-) cotransporter NBCn1 for duodenal defence against acid and colonic mucus release. NBCn1 was localized to the basolateral membrane of duodenal villous enterocytes and of colonic crypt cells, with predominant expression in goblet cells. Duodenal villous enterocyte intracellular pH was studied before and during a luminal acid load by two-photon microscopy in exteriorized, vascularly perfused, indicator (SNARF-1 AM)-loaded duodenum of isoflurane-anaesthetized, systemic acid-base-controlled mice. Acid-induced HCO3(-) secretion was measured in vivo by single-pass perfusion and pH-stat titration. After a luminal acid load, NBCn1-deficient duodenocytes were unable to recover rapidly from intracellular acidification and could not respond adequately with protective HCO3(-) secretion. In the colon, build-up of the mucus layer was delayed, and a decreased thickness of the adherent mucus layer was observed, suggesting that basolateral HCO3(-) uptake is essential for optimal release of mucus. The electroneutral Na(+)-HCO3(-) cotransporter NBCn1 displays a differential cellular distribution in the murine intestine and is essential for HCO3(-)-dependent mucosal protective functions, such as recovery of intracellular pH and HCO3(-) secretion in the duodenum and secretion of mucus in the colon.

Apoptosis of regulatory T lymphocytes is increased in chronic inflammatory bowel disease and reversed by anti-TNFα treatment.

BACKGROUND AND AIMS: Inappropriate immune responses contribute to the continuous stimulation of the intestinal immune system in chronic inflammatory bowel disease (IBD). Among several pathogenic factors, a numerical deficiency of regulatory T (Treg) cells has been suggested to lead to an insufficient compensation of chronically activated T lymphocytes. This study was conducted to investigate whether increased apoptosis contributes to Treg cell deficiency in IBD and whether successful treatment with antitumour necrosis factor α (TNFα) is achieved by reducing of Treg cell apoptosis. METHODS: Apoptosis of CD4(+)Foxp3(+) Treg cells in tissue sections of patients with active IBD was analysed by immunohistochemistry and TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labelling) staining. Apoptosis of peripheral blood CD4(+)CD25(+)Foxp3(+) Treg cells was investigated by flow cytometry and annexin-V staining. In addition, caspase activity and apoptosis were measured in sera of patients with IBD treated with anti-TNFα by a luminometric caspase enzyme assay. RESULTS: It is demonstrated that patients with active IBD revealed increased apoptosis of local CD4(+)Foxp3(+) Treg cells in the inflamed mucosa compared with non-inflamed control colon tissue. Moreover, in peripheral blood a reduced frequency and increased apoptosis of Treg cells were found and accompanied by elevated caspase activity in the serum. During anti-TNFα treatment, Treg cell apoptosis declined in close correlation with elevated peripheral Treg cell numbers and a decrease of caspase activation and disease activity. CONCLUSIONS: These data suggest that increased apoptosis of Treg cells plays a potentially important role in the pathogenesis of IBD and can be reversed by anti-TNFα treatment. Measurement of Treg cell apoptosis and serum caspase activity might therefore represent promising tools for monitoring disease activity and treatment response in patients with IBD.

ECCO Guidelines on Therapeutics in Ulcerative Colitis: Surgical Treatment.

This is the second of a series of two articles reporting the European Crohn's and Colitis Organisation [ECCO] evidence-based consensus on the management of adult patients with ulcerative colitis [UC]. The first article is focused on medical management, and the present article addresses medical treatment of acute severe ulcerative colitis [ASUC] and surgical management of medically refractory UC patients, including preoperative optimisation, surgical strategies, and technical issues. The article provides advice for a variety of common clinical and surgical conditions. Together, the articles represent an update of the evidence-based recommendations of the ECCO for UC.

News from the end of the gut--how the highly segmental pattern of colonic HCO3⁻ transport relates to absorptive function and mucosal integrity.

A number of transport mechanisms in the colonic epithelium contribute to HCO3⁻ movement across the apical and basolateral membranes, but this ion has been largely regarded as a by-product of the transport functions it is involved in, such as NaCl or short chain fatty acid (SCFA) absorption. However, emerging data points to several specific roles of HCO3⁻ for colonic epithelial physiology, including pH control in the colonic surface microenvironment, which is important for transport and immune functions, as well as the secretion and the rheological properties of the mucus gel. Furthermore, recent studies have demonstrated that colonic HCO3⁻ transporters are expressed in a highly segmental as well as species-specific manner. This review summarizes recently gathered information on the functional anatomy of the colon, the roles of HCO3⁻ in the colonic epithelium, colonic mucosal integrity, and the expression and function of HCO3⁻ transporting mechanisms in health and disease.

Inflammatory Cutaneous Lesions in Inflammatory Bowel Disease Treated With Vedolizumab or Ustekinumab: An ECCO CONFER Multicentre Case Series.

This was a multicentre case series supported by the European Crohn's and Colitis Organisation [ECCO] and performed as part of the Collaborative Network of Exceptionally Rare case reports [CONFER] project. The aim was to report on whether cutaneous lesions associated with inflammatory bowel disease [IBD] and refractory to standard medical therapy including anti-tumour necrosis factors [anti-TNFs], would respond to the newer biologic agents ustekinumab [UST] or vedolizumab [VDZ]. This report includes 28 patients with cutaneous lesions from 14 centres, all of whom had failed immunomodulator and anti-TNF therapy. Metastatic Crohn's disease [MCD] was diagnosed in 10 patients: UST led to remission in five cases and partial response in four cases, with a single report of VDZ inducing remission. All cases of MCD treated with UST responded after the first or second dose, and the median time for the five cases that attained remission was 5 months. Pyoderma gangrenosum [PG] was diagnosed in four cases: three of these attained remission with UST [median time to remission 4 months] and one case did not respond to VDZ. There were seven cases of erythema nodosum [EN]: UST led to remission in four cases and partial response in 1 case whilst VDZ had partial response in 2 cases and non-response in two cases. There were seven single cases of other inflammatory lesions. In summary, UST appears to be useful for different cutaneous lesions including MCD, PG, and EN, whereas VDZ does not appear to be useful for lesions that are independent of disease activity.

ECCO Guidelines on Therapeutics in Crohn's Disease: Surgical Treatment.

This article is the second in a series of two publications relating to the European Crohn's and Colitis Organisation [ECCO] evidence-based consensus on the management of Crohn's disease. The first article covers medical management; the present article addresses surgical management, including preoperative aspects and drug management before surgery. It also provides technical advice for a variety of common clinical situations. Both articles together represent the evidence-based recommendations of the ECCO for Crohn's disease and an update of previous guidelines.

Secretagogue stimulation enhances NBCe1 (electrogenic Na(+)/HCO(3)(-) cotransporter) surface expression in murine colonic crypts.

A Na(+)/HCO(3)(-) cotransporter (NBC) is located in the basolateral membrane of the gastrointestinal epithelium, where it imports HCO(3)(-) during stimulated anion secretion. Having previously demonstrated secretagogue activation of NBC in murine colonic crypts, we now asked whether vesicle traffic and exocytosis are involved in this process. Electrogenic NBCe1-B was expressed at significantly higher levels than electroneutral NBCn1 in colonic crypts as determined by QRT-PCR. In cell surface biotinylation experiments, a time-dependent increase in biotinylated NBCe1 was observed, which occurred with a peak of +54.8% after 20 min with forskolin (P < 0.05) and more rapidly with a peak of +59.8% after 10 min with carbachol (P < 0.05) and which corresponded well with the time course of secretagogue-stimulated colonic bicarbonate secretion in Ussing chamber experiments. Accordingly, in isolated colonic crypts pretreated with forskolin and carbachol for 10 min, respectively, and subjected to immunohistochemistry, the NBCe1 signal showed a markedly stronger colocalization with the E-cadherin signal, which was used as a membrane marker, compared with the untreated control. Cytochalasin D did not change the observed increase in membrane abundance, whereas colchicine alone enhanced NBCe1 membrane expression without an additional increase after carbachol or forskolin, and LY294002 had a marked inhibitory effect. Taken together, our results demonstrate a secretagogue-induced increase of NBCe1 membrane expression. Vesicle traffic and exocytosis might thus represent a novel mechanism of intestinal NBC activation by secretagogues.

Myeloid-derived suppressor cells in inflammatory bowel disease: a new immunoregulatory pathway.

BACKGROUND & AIMS: CD11b(+)Gr-1(+) myeloid-derived suppressor cells (MDSCs) have been shown to cause T-cell tolerance in tumor-bearing mice; however, little is known about the role of MDSCs in chronic inflammation. Here, for the first time, we have identified and analyzed their role in inflammatory bowel disease (IBD). METHODS: Repetitive adoptive transfer of clone 4/T-cell receptor (CL4-TCR) transgenic CD8(+) T cells into VILLIN-hemagglutinin (HA) transgenic mice was performed on days 1, 12, and 27. Recipient mice were analyzed for immunopathology, HA-specific CD8(+) T-cell responses, and CD11b(+)Gr-1(+) MDSCs (frequency, phenotype, expression analysis, and in vitro as well as in vivo function). In addition, peripheral blood from patients with active Crohn's disease and ulcerative colitis was examined for the presence and function of human MDSCs denoted as CD14(+)HLA-DR(-/low) cells. RESULTS: Repetitive transfer of HA-specific CD8(+) T cells prevented VILLIN-HA recipient mice from development of severe enterocolitis, which is seen after a single transfer of T cells. Repeated transfer of antigen-specific T cells led to an increase in the frequency of nitric oxide synthase 2 and arginase-expressing CD11b(+)Gr-1(+) MDSCs in spleen and intestine of VILLIN-HA mice with immunosuppressive function. Cotransfer of MDSCs with HA-specific CD8(+) T cells into naive VILLIN-HA mice ameliorated enterocolitis, indicating a direct immune regulatory effect of MDSCs on induction of IBD by antigen-specific T cells. Finally, an increase in the frequency of human MDSCs with suppressor function was observed in peripheral blood from patients with IBD. CONCLUSIONS: These results identify MDSCs as a new immune regulatory pathway in IBD.

Knockout mouse models for intestinal electrolyte transporters and regulatory PDZ adaptors: new insights into cystic fibrosis, secretory diarrhoea and fructose-induced hypertension.

Knockout mouse models have provided key insights into the physiological significance of many intestinal electrolyte transporters. This review has selected three examples to highlight the importance of knockout mouse technology in unravelling complex regulatory relationships important for the understanding of human diseases. Genetic ablation of the cystic fibrosis transmembrane conductance regulator (CFTR) has created one of the most useful mouse models for understanding intestinal transport. Recent work has provided an understanding of the key role of the CFTR anion channel in the regulation of HCO(3)(-) secretion, and the important consequences that a defect in HCO(3)(-) output may have on the viscoelastic properties of mucus, on lipid absorption and on male and female reproductive function. The regulation of CFTR activity, and also that of the intestinal salt absorptive transporter NHE3, occurs via the formation of PSD95-Drosophila homologue Discs-large-tight junction protein ZO-1 (PDZ) adaptor protein-mediated multiprotein complexes. The recent generation of knockout mice for three members of the sodium-hydrogen regulatory factor (NHERF) family of PDZ adaptor proteins, namely NHERF1 (EBP50), NHERF2 (E3KARP) and NHERF3 (PDZK1), has helped to explain why NHERF1 is essential for both normal and mutant CFTR function. In addition, they have provided new insight into the molecular mechanisms of secretory diarrhoeas. Genetic ablation of members of the recently discovered Slc26 anion transporter gene family not only reproduced the phenotype of the genetic diseases that led to the discovery of the gene family, but also resulted in new insights into complex human diseases such as secretory diarrhoea, fructose-induced hypertension and urolithiasis.

Fecal calprotectin is significantly linked to azathioprine metabolite concentrations in Crohn's disease.

BACKGROUND: The value of therapeutic drug monitoring during azathioprine (AZA) therapy with respect to clinical outcomes has been convincingly demonstrated in recent meta-analyses. However, the association between AZA metabolites and the mucosal state in inflammatory bowel disease is largely unclear. AIMS: We investigated the association between AZA's active metabolite 6-thioguanine nucleotides (6-TGN) and fecal calprotectin (FC) as a well-validated surrogate marker of mucosal inflammation in patients with Crohn's disease (CD) on AZA monotherapy. PATIENTS AND METHODS: Of 443 6-TGN measurements, 140 values from 88 patients with CD on AZA monotherapy visiting the inflammatory bowel disease outpatient clinic between 2009 and 2016 were retrospectively analyzed. In a subcohort with serial 6-TGN measurements, longitudinal FC measurements in patients with versus without intervention (dose increase, allopurinol, and education) were assessed. RESULTS: In patients with 6-TGN concentrations within a predefined range (250-450 pmol/8×10 red blood cells), FC was significantly lower (median: 119.5 vs. 327.2 mg/kg, P=0.003), and hemoglobin as well as serum protein concentrations were significantly higher than in patients with 6-TGN outside of this range. C-reactive protein and transferrin saturation were not different. In the longitudinal cohort, 6-TGN increased in the intervention group, but only a minority reached the defined range; no significant change in FC was observed. CONCLUSION: This study is the first to show that in patients with CD receiving AZA monotherapy, 6-TGN concentrations within a defined range (250-450 pmol/8×10 red blood cells) are associated with significantly lower FC. A treat-to-target concept directed by 6-TGN to reach mucosal healing may thus be a promising approach (DRKS00013246).

Quality of Life Is Associated With Wearable-Based Physical Activity in Patients With Inflammatory Bowel Disease: A Prospective, Observational Study.

OBJECTIVES: Patient-reported outcomes such as quality of life are gaining importance in the assessment of patients suffering from inflammatory bowel disease (IBD). The association of objectively measured physical activity and quality of life in patients with IBD has not been studied in depth. To investigate the association of disease-specific quality of life and physical activity as well as clinical and biochemical disease activity in patients with IBD. METHODS: A total of 91 patients with IBD were stratified into 4 groups (Crohn's disease and ulcerative colitis, in remission and with moderate-severe activity, respectively) and evaluated in terms of disease-specific quality of life (Inflammatory Bowel Disease Questionnaire [IBDQ]), physical activity (accelerometry), body composition (bioelectrical impedance analysis), as well as clinical (Harvey-Bradshaw Index and Simple Clinical Colitis Activity Index) and biochemical (C-reactive protein and fecal calprotectin) parameters of disease activity. RESULTS: In patients with moderate-severe disease activity, the IBDQ was significantly lower as compared to patients in remission (Mann-Whitney U test and Kruskal-Wallis test, P < 0.001). The physical activity level was higher in remission than in active disease (Mann-Whitney U test, P < 0.05). The IBDQ was significantly correlated with the duration of strenuous physical activity per day (P = 0.029178, r = 0.235), skeletal muscle mass (P = 0.033829, r = 0.229), and biomarkers of inflammation (C-reactive protein: P < 0.005, r = -0.335 and fecal calprotectin: P < 0.005, r = -0.385). DISCUSSION: In this prospective, cross-sectional study, disease-specific quality of life was significantly associated with accelerometrically determined physical activity and disease activity in patients with IBD. This may be related to a reciprocal impact of these factors (DRKS00011370).

The impact of technical and clinical factors on fecal microbiota transfer outcomes for the treatment of recurrent Clostridioides difficile infections in Germany.

Introduction: Fecal microbiota transfer (FMT) is highly effective in the treatment and prevention of recurrent Clostridioides difficile infection (rCDI) with cure rates of about 80% after a single treatment. Nevertheless, the reasons for failure in the remaining 20% remain largely elusive. The aim of the present study was to investigate different potential clinical predictors of response to FMT in Germany. Methods: Information was extracted from the MicroTrans Registry (NCT02681068), a retrospective observational multicenter study, collecting data from patients undergoing FMT for recurrent or refractory CDI in Germany. We performed binary logistic regression with the following covariates: age, gender, ribotype 027, Eastern Co-operative Oncology Group score, immunosuppression, preparation for FMT by use of proton pump inhibitor, antimotility agents and bowel lavage, previous recurrences, severity of CDI, antibiotic induction treatment, fresh or frozen FMT preparation, and route of application. Results: Treatment response was achieved in 191/240 evaluable cases (79.6%) at day 30 (D30) post FMT and 78.1% at day 90 (D90) post FMT. Assessment of clinical predictors for FMT failure by forward and confirmatory backward-stepwise regression analysis yielded higher age as an independent predictor of FMT failure (p = 0.001; OR 1.060; 95%CI 1.025-1.097). Conclusion: FMT in Germany is associated with high cure rates at D30 and D90. No specific pre-treatment, preparation or application strategy had an impact on FMT success. Only higher age was identified as an independent risk factor for treatment failure. Based on these and external findings, future studies should focus on the assessment of microbiota and microbiota-associated metabolites as factors determining FMT success.

cAMP-dependent and cholinergic regulation of the electrogenic intestinal/pancreatic Na+/HCO3- cotransporter pNBC1 in human embryonic kidney (HEK293) cells.

BACKGROUND: The renal (kNBC1) and intestinal (pNBC1) electrogenic Na+/HCO3- cotransporter variants differ in their primary structure, transport direction, and response to secretagogues. Previous studies have suggested that regulatory differences between the two subtypes can be partially explained by unique consensus phosphorylation sites included in the pNBC1, but not the kNBC1 sequence. After having shown activation of NBC by carbachol and forskolin in murine colon, we now investigated these pathways in HEK293 cells transiently expressing a GFP-tagged pNBC1 construct. RESULTS: Na+- and HCO3-dependent pHi recovery from an acid load (measured with BCECF) was enhanced by 5-fold in GFP-positive cells compared to the control cells in the presence of CO2/HCO3-. Forskolin (10(-5) M) had no effect in untransfected cells, but inhibited the pHi recovery in cells expressing pNBC1 by 62%. After preincubation with carbachol (10(-4) M), the pHi recovery was enhanced to the same degree both in transfected and untransfected cells, indicating activation of endogenous alkalizing ion transporters. Acid-activated Na+/HCO3- cotransport via pNBC1 expressed in renal cells is thus inhibited by cAMP and not affected by cholinergic stimulation, as opposed to the findings in native intestinal tissue. CONCLUSION: Regulation of pNBC1 by secretagogues appears to be not solely dependent on its primary structure, but also on properties of the cell type in which it is expressed.