ABC transporter trafficking in rat liver induced by cAMP or taurocholate and [35 S]methionine metabolic labeling followed by subcellular fractionation were used to identify and characterize intrahepatic pools of ABC transporters. ABC transporter trafficking induced by cAMP or taurocholate is a physiologic response to a temporal demand for increased bile secretion. Administration of cAMP or taurocholate to rats increased amounts of SPGP, MDR1, and MDR2 in the bile canalicular membrane by 3-fold; these effects abated after 6 h and were insensitive to prior treatment of rats with cycloheximide. Half-lives of ABC transporters were 5 days, which suggests cycling of ABC transporters between canalicular membrane and intrahepatic sites before degradation. In vivo [35 S]methionine labeling of rats followed by immunoprecipitation of (sister of Pglycoprotein) (SPGP) from subcellular liver fractions revealed a steady state distribution after 20 h of SPGP between canalicular membrane and a combined endosomal fraction. After mobilization of transporters from intrahepatic sites with cAMP or taurocholate, a significant increase in the amount of ABC transporters in canalicular membrane vesicles was observed, whereas the decrease in the combined endosomal fraction remained below detection limits in Western blots. This observation is in accordance with relatively large intracellular ABC transporter pools compared with the amount present in the bile canalicular membrane. Furthermore, trafficking of newly synthesized SPGP through intrahepatic sites was accelerated by additional administration of cAMP but not by taurocholate, indicating two distinct intrahepatic pools. Our data indicate that ABC transporters cycle between the bile canaliculus and at least two large intrahepatic ABC transporter pools, one of which is mobilized to the canalicular membrane by cAMP and the other, by taurocholate. In parallel to regulation of other membrane transporters, we propose that the "cAMP-pool" in hepatocytes corresponds to a recycling endosome, whereas recruitment from the "taurocholate-pool" involves a hepatocyte-specific mechanism.The bile canalicular membrane of the mammalian hepatocyte contains several primary active transporters that couple ATP hydrolysis to the transport of specific substrates into the bile canaliculus (1-4). These transporters are members of the superfamily of ATP binding cassette (ABC) 1 membrane transport proteins (5) and currently include P-glycoprotein (MDR1) for organic cations (6), MDR2 for phosphatidylcholine translocation (7, 8), sister of P-glycoprotein (SPGP), the canalicular bile salt export pump (BSEP) (9), and MRP2 for non-bile acid organic anions (10).Recent studies indicate that the amount of each ABC transporter in the canalicular membrane is regulated by the physiological demand to secrete bile acids. Intravenous administration to rats of dibutyryl-cAMP (Bt 2 cAMP) or taurocholate (TC) rapidly and selectively increased the functional activity and amount of each ABC transporter in the canalicular membrane; ...
INTRODUCTION:Irritable bowel syndrome (IBS) includes diarrhea-predominant (IBS-D) and constipation-predominant (IBS-C) subtypes. We combined breath testing and stool microbiome sequencing to identify potential microbial drivers of IBS subtypes.METHODS:IBS-C and IBS-D subjects from 2 randomized controlled trials (NCT03763175 and NCT04557215) were included. Baseline breath carbon dioxide, hydrogen (H2), methane (CH4), and hydrogen sulfide (H2S) levels were measured by gas chromatography, and baseline stool microbiome composition was analyzed by 16S rRNA sequencing. Microbial metabolic pathways were analyzed using Kyoto Encyclopedia of Genes and Genomes collection databases.RESULTS:IBS-C subjects had higher breath CH4 that correlated with higher gut microbial diversity and higher relative abundance (RA) of stool methanogens, predominantly Methanobrevibacter, as well as higher absolute abundance of Methanobrevibacter smithii in stool. IBS-D subjects had higher breath H2 that correlated with lower microbial diversity and higher breath H2S that correlated with higher RA of H2S-producing bacteria, including Fusobacterium and Desulfovibrio spp. The predominant H2 producers were different in these distinct microtypes, with higher RA of Ruminococcaceae and Christensenellaceae in IBS-C/CH4+ (which correlated with Methanobacteriaceae RA) and higher Enterobacteriaceae RA in IBS-D. Finally, microbial metabolic pathway analysis revealed enrichment of Kyoto Encyclopedia of Genes and Genomes modules associated with methanogenesis and biosynthesis of methanogenesis cofactor F420 in IBS-C/CH4+ subjects, whereas modules associated with H2S production, including sulfate reduction pathways, were enriched in IBS-D.DISCUSSION:Our findings identify distinct gut microtypes linked to breath gas patterns in IBS-C and IBS-D subjects, driven by methanogens such as M. smithii and H2S producers such as Fusobacterium and Desulfovibrio spp, respectively.
Abdominal pain is a common reason for referral to a gastroenterologist. The workup of patients with chronic abdominal pain can be extremely challenging as clinicians are responsible for determining whether the patient can be observed or treated symptomatically or this abdominal pain heralds a more systemic disease. The differential is typically wide and given the innervation of the abdomen, localization of abdominal pain does not always provide clear insight into the etiology. This review attempts to help the gastroenterologist narrow down that broad differential and focus on key elements of the patient visit. We emphasize the importance of a detailed history from the patient, along with review-specific details of their history and physical examination that can clue one in about the etiology of the abdominal pain. We review the causes of diffuse abdominal pain that may not first be considered along with uncommon causes of localized abdominal pain. We also review the functional causes of abdominal pain and the importance of identifying these disorders, to avoid unnecessary testing that commonly occurs with these patients.
Endoscopists performing moderate sedation should continue midazolam rather than switching to diphenhydramine in patients who do not achieve adequate sedation with usual doses of midazolam and an opioid. (Clinical trial registration number: NCT01769586.).
Background Recent data substantiate the importance of acute gastroenteritis in the development of irritable bowel syndrome (IBS). An animal model of postinfectious IBS determined the importance of cytolethal distending toxin B (CdtB) during live Campylobacter jejuni infection and its development of autoimmunity to vinculin. In this study, we examine whether subcutaneous exposure to CdtB alone is sufficient to produce the postinfectious IBS effect and autoimmunity. Methods Sixty adult Sprague Dawley rats were randomized into 2 groups to receive subcutaneous injection of either CdtB or vehicle and administered a booster injection of the same product 3 weeks later. Serum was collected for anti‐CdtB and anti‐vinculin titers. Duodenal and ileal luminal contents for total eubacterial qPCR, and ileal bowel segments were harvested for vinculin and ileal expression. In a second experiment, 4 adult, Sprague Dawley rats were injected with either Cy7‐labeled anti‐CdtB and anti‐vinculin antibodies were injected into the tail vein and imaged to determine organ localization of the antibodies. Key Results Rats that received CdtB increased in serum anti‐CdtB after injection. CdtB exposure also precipitated significant elevation in anti‐vinculin antibodies (P < .001). This was associated with a reduction in intestinal vinculin expression (P < .001) that negatively correlated with serum anti‐CdtB levels. CdtB exposure was also associated with greater levels of duodenal (P < .001) and ileal (P < .01) bacteria by qPCR that positively correlated with anti‐CdtB levels. Conclusions and Inferences Rats injected with CdtB developed a postinfectious IBS‐like phenotype and autoimmunity to vinculin with corresponding reduction in intestinal vinculin expression.
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