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Background & Aims: Irritable bowel syndrome (IBS) is subtyped as IBS with diarrhea (IBS-D) or IBS with constipation (IBS-C) based on Rome II guidelines. The remaining group is considered as having mixed IBS (IBS-M). There is no standard definition of an alternator (IBS-A), in which bowel habit changes over time. Our aim was to use Rome II criteria to prospectively assess change in bowel habit for more than 1 year to understand IBS-A. Methods: Female patients (n = 317) with IBS entering a National Institutes of Health treatment trial were studied at baseline with questionnaires and 2-week daily diary cards of pain and stool frequency and consistency. Studies were repeated at the end of treatment (3 months) and at four 3-month intervals for one more year. Algorithms to classify subjects into IBS-D, IBS-C, and IBS-M groups used diary card information and modified Rome II definitions. Changes in bowel habit at 3-month intervals were then assessed using these surrogate diary card measures. Results: At baseline, 36% had IBS-D, 31% IBS-M, and 34% IBS-C. Except for stool frequency, there were no differences between groups. While the proportion of subjects in each subgroup remained the same over the year, most individuals (more than 75%) changed to either of the other 2 subtypes at least once. IBS-M was the least stable (50% changed out by 12 weeks). Patients were more likely to transition between IBS-M and IBS-C than between IBS-D and IBS-M. Notably, only 29% switched between the IBS-D and IBS-C subtypes over the year. Conclusions: While the proportion of subjects in each of the IBS subtypes stays the same, individuals commonly transition between subtypes, particularly between IBS-M and IBS-C. We recommend that IBS-A be defined as at least one change between IBS-D and IBS-C by Rome II criteria over a 1-year period.

The endocytic pathway of the secretin receptor, a class II GPCR, is unknown. Some class I G protein-coupled receptors (GPCRs), such as the beta(2)-adrenergic receptor (beta(2)-AR), internalize in clathrin-coated vesicles and this process is mediated by G protein-coupled receptor kinases (GRKs), beta-arrestin, and dynamin. However, other class I GPCRs, for example, the angiotensin II type 1A receptor (AT(1A)R), exhibit different internalization properties than the beta(2)-AR. The secretin receptor, a class II GPCR, is a GRK substrate, suggesting that like the beta(2)-AR, it may internalize via a beta-arrestin and dynamin directed process. In this paper we characterize the internalization of a wild-type and carboxyl-terminal (COOH-terminal) truncated secretin receptor using flow cytometry and fluorescence imaging, and compare the properties of secretin receptor internalization to that of the beta(2)-AR. In HEK 293 cells, sequestration of both the wild-type and COOH-terminal truncated secretin receptors was unaffected by GRK phosphorylation, whereas inhibition of cAMP-dependent protein kinase mediated phosphorylation markedly decreased sequestration. Addition of secretin to cells resulted in a rapid translocation of beta-arrestin to plasma membrane localized receptors; however, secretin receptor internalization was not reduced by expression of dominant negative beta-arrestin. Thus, like the AT(1A)R, secretin receptor internalization is not inhibited by reagents that interfere with clathrin-coated vesicle-mediated internalization and in accordance with these results, we show that secretin and AT(1A) receptors colocalize in endocytic vesicles. This study demonstrates that the ability of secretin receptor to undergo GRK phosphorylation and beta-arrestin binding is not sufficient to facilitate or mediate its internalization. These results suggest that other receptors may undergo endocytosis by mechanisms used by the secretin and AT(1A) receptors and that kinases other than GRKs may play a greater role in GPCR endocytosis than previously appreciated.

The secretin receptor is a member of a structurally distinct class of G protein-coupled receptors designated as Class II. The molecular mechanisms of secretin receptor signal termination are unknown. Using transiently transfected HEK 293 cells expressing the secretin receptor, we investigated its mechanisms of desensitization. Binding of [125I]-secretin to plasma membranes of receptor-expressing cells was specific, with a Kd of 2 nM. Secretin evoked an increase in cellular cAMP with an EC50 of 0.4 nM. The response was maximal by 20 min and desensitized rapidly and completely. Immunoprecipitation of a functional, N-terminal epitope-tagged secretin receptor was used to demonstrate agonist-dependent receptor phosphorylation, with an EC50 of 14 nM. Pretreatment with protein kinase A or C inhibitors failed to alter secretin-stimulated cAMP accumulation. G protein-coupled receptor kinases (GRKs) are known to be involved in the desensitization of Class I G protein-coupled receptors; therefore, the effect of cotransfection of GRKs on secretin-stimulated cAMP signaling and phosphorylation was evaluated. GRKs 2 and 5 were the most potent at augmenting desensitization, causing a 40% reduction in the maximal cAMP response to secretin. GRK 5 also caused a shift in the EC50 to the right (p < 0.05). GRK 4 and GRK 6 did not alter dose-dependent signaling, and GRK 3 was intermediate in effect. Receptor phosphorylation correlated with desensitization for each GRK studied, whereas second messenger-dependent kinase phosphorylation appeared to be less important in secretin receptor signal termination. We demonstrate agonist-dependent secretin receptor phosphorylation coincident with profound receptor desensitization of the signaling function in HEK 293 cells, suggesting a role for receptor phosphorylation in this paradigm. Although GRK activity appears important in secretin receptor desensitization in HEK 293 cells, protein kinases A and C appear to play only a minor role. These results demonstrate that the GRK-arrestin system regulates Class II G protein-coupled receptors.

IntroductionVedolizumab (VDZ) binds to α4β7integrin and selectively blocks gut-specific lymphocyte trafficking. Selectivity could reduce the risk of respiratory tract infections (RTIs) compared with therapies causing systemic immunosuppression (e.g. anti-tumour necrosis factor-alpha [TNFα] agents). The annual pneumonia rate in inflammatory bowel disease is higher than in healthy individuals (13.8/1000 vs 7.6/1000; incident rate ratio 1.82; 95% CI: 1.75–1.88) and the risk is increased with anti-TNFα treatment (odds ratio 1.28; 95% CI: 1.08–1.52).1We report rates of RTIs associated with VDZ treatment in clinical trials.MethodData from GEMINI 1 (ulcerative colitis; UC) and GEMINI 2 (Crohn’s disease; CD) and an ongoing open-label extension (OLE; data cut-off: May 2015; UC and CD) were used to calculate rates of lower RTIs (LRTIs) and upper RTIs (URTIs). A Cox proportional hazards model was used to identify potential predictors of these adverse events (AEs) in a pooled analysis of GEMINI 1/2.ResultsIn GEMINI 1/2 (n=1434, VDZ; n=297, placebo) and in the OLE (n=2243, all VDZ), mean (SD) ages were 37.9 (12.7) years and 39.1 (13.2) years; 47.8% and 49.7% were female sex; 17.2% and 18.1% were current smokers and 27.3% and 26.3% were former smokers, respectively. In GEMINI 1/2, exposure-adjusted incidence rates per 100 patient-years [IRs] of LRTIs were similar in VDZ and placebo groups: LRTIs overall 7.7 vs 8.5; pneumonia 1.0 vs 1.2; bronchopneumonia <0.1 vs 0.6 and primary atypical pneumonia <0.1 vs 0, respectively. The IR of URTIs overall was higher with VDZ (38.7) than with placebo (33.0). OLE IRs were no greater than for GEMINI 1/2: LRTIs overall 5.0; URTIs overall 23.5. Most RTIs were not serious. Two LRTIs (VDZ, GEMINI 2) and two URTIs (one in OLE; one in GEMINI 2) resulted in discontinuation. Predictors of increased LRTI incidence were: current/former smoker (hazard ratio [HR] 1.97; 95% CI: 1.17–3.31; p=0.0110 and 1.74; 95% CI 1.06–2.87, p=0.0291, respectively), female sex (HR 1.84; 95% CI: 1.19–2.83; p=0.0058) and prior anti-TNFα use (HR 1.70; 95% CI: 1.06–2.73; p=0.0281). Predictors of URTIs were: current smoker (HR: 1.35; 95% CI: 1.04–1.75; p=0.0225), concomitant narcotic use (HR: 1.30; 95% CI: 1.04–1.64; p=0.0215) and prior anti-TNFα use (HR: 1.50; 95% CI: 1.20–1.88; p=0.0004).ConclusionIn this post hoc analysis, VDZ treatment of UC/CD was not associated with an increased incidence of LRTIs, including pneumonia, compared with placebo.W.Palo is now at Abbvie Inc., North Chicago, IL, USAReference. Long MD, et al. Am J Gastroenterol2013;108:240Disclosure of InterestB. Feagan Conflict with: Abbott/AbbVie, Amgen, Astra Zeneca, Bristol-Myers Squibb (BMS), Janssen Biotech (Centocor), JnJ/Janssen, Roche/Genentech, Millennium, Pfizer, Receptos, Santarus, Sanofi, Tillotts, UCB Pharma, Conflict with: Abbott/AbbVie, ActoGeniX, Akros, Albireo Pharma, Amgen, Astra Zeneca, Avaxia Biologics Inc., Avir Pharma, Axcan, Baxter Healthcare Corp., Biogen Idec, Boehringer-Ingelheim, Bristol-Myers Squibb, Calypso Biotech, Celgene, Elan/Biogen, enGene, Ferring Pharma, Roche/Genentech, gICare Pharma, Gilead, Given Imaging Inc., GSK, Ironwood Pharma, Janssen Biotech (Centocor), JnJ/Janssen, Kyowa Hakko Kirin Co Ltd., Lexicon, Lilly, Lycera BioTech, Merck, Mesoblast Pharma, Millennium, Nektar, Nestles, Novo Nordisk, Pfizer, Prometheus Therapeutics and Diagnostics, Protagonist, Receptos, Salix Pharma, Serono, Shire, Sigmoid Pharma, Synergy Pharma Inc., Takeda, Teva Pharma, TiGenix, Tillotts, UCB Pharma, Vertex Pharma, VHsquared Ltd., Warner Chilcott, Wyeth, Zealand, Zyngenia, Conflict with: director of Robarts Clinical Trials; membership (scientific advisory board) of Abbott/AbbVie, Amgen, Astra Zeneca, Avaxia Biologics Inc., Bristol-Myers Squibb, Celgene, Centocor Inc., Elan/Biogen, Ferring, JnJ/Janssen, Merck, Nestles, Novartis, Novo Nordisk, Pfizer, Prometheus Laboratories, Protagonist, Salix Pharma, Takeda, Teva, TiGenix, Tillotts Pharma AG, UCB Pharma, F Bhayat Conflict with: Takeda Development Centre Europe Ltd, J Khalid Conflict with: Takeda Development Centre Europe Ltd, W Palo Conflict with: Takeda Development Centre Americas, Inc.; Abbvie, Inc., A Blake Conflict with: Takeda Development Centre Europe Ltd, M Shetzline Conflict with: Takeda Pharmaceuticals International Co., S Travis Conflict with: AbbVie, IOIBD, Lilly, UCB, Vifor, and Norman Collison Foundation, Conflict with: AbbVie, Amgen, Biogen, Boehringer Ingelheim, Bristol-Myers Squibb, Celgene, Chemocentryx, Cosmo, Ferring, Giuliani SpA, GlaxoSmithKline, Janssen, Lilly, MSD, Neovacs, NovoNordisk, Norman Collison Foundation, Novartis, NPS Pharmaceuticals, Pfizer, Proximagen, Receptos, Shire, Sigmoid Pharma, Takeda, Topivert, UCB, VHsquared and Vifor, Conflict with: Oxford University Hospitals NHS Foundation Trust and the University of Oxford, Conflict with: Lecture fee(s): AbbVie, Amgen, Biogen, Ferring, Takeda