NE-activated β2-AR/β-arrestin 2/Src pathway mediates duodenal hyperpermeability induced by water-immersion restraint stress

Stress causes a rapid spike in norepinephrine (NE) levels, leading to gastrointestinal dysfunction. NE reduces the expression of tight junctions (TJs) and aggravates intestinal mucosal damage, but the regulatory mechanism is still unclear. The present study aimed to investigate the molecular mechanisms underlying the regulation of stress-associated duodenal hyperpermeability by NE. Fluorescein isothiocyanate-dextran permeability, transepithelial resistance, immunofluorescence, Western blot, and high-performance liquid chromatography analysis were used in water-immersion restraint stress (WIRS) rats in this study. The results indicate that the duodenal permeability, degradation of TJs, mucosal NE, and β₂-adrenergic receptor (β₂-AR) increased in WIRS rats. The duodenal intracellular cyclic adenosine monophosphate levels were decreased, whereas the expression of β-arrestin 2 negatively regulates G protein-coupled receptors signaling, was significantly increased. Src recruitment was mediated by β-arrestin; thus, the levels of Src kinase activation were enhanced in WIRS rats. NE depletion, β₂-AR, or β-arrestin 2 blockade significantly decreased mucosal permeability and increased TJs expression, suggesting improved mucosal barrier function. Moreover, NE induced an increased duodenal permeability of normal rats with activated β-arrestin 2/Src signaling, which was significantly inhibited by β₂-AR blockade. The present findings demonstrate that the enhanced NE induced an increased duodenal permeability in WIRS rats through the activated β₂-AR/β-arrestin 2/Src pathway. This study provides novel insight into the molecular mechanism underlying the regulation of NE on the duodenal mucosal barrier and a new target for treating duodenal ulcers induced by stress.

Confocal laser endomicroscopy reveals alterations in duodenal permeability in patients with acute pancreatitis

Objective

Intestinal permeability increases during the course of acute pancreatitis (AP). We assessed duodenal permeability alterations in patients with AP by confocal laser endomicroscopy (CLE).

Methods

Thirty patients with AP underwent CLE evaluation of the antral and duodenal mucosa. Images were graded based on the appearance of capillaries and the degree of fluorescein leakage.

Results

Patients with AP had increased duodenal mucosal permeability that could be detected by CLE. The mucosal permeability progressively increased in the gastric antrum, duodenal bulb, and descending duodenum. The CLE parameters in the antrum and duodenal bulb were not significantly different between patients with mild and severe AP. The CLE grades in the descending duodenum were higher in patients with severe than mild AP. The C-reactive protein level in AP was positively correlated with the permeability in the duodenal bulb and descending duodenum, while the computed tomography severity index score was positively correlated with the mucosal permeability in the duodenal bulb and descending duodenum.

Conclusion

CLE revealed increased duodenal permeability in patients with AP. Higher permeability in the descending duodenum was observed in severe than mild AP. Further large-scale studies are needed to confirm the relationship between altered duodenal permeability and the severity of AP.

Relationship between bile salts, bacterial translocation, and duodenal mucosal integrity in functional dyspepsia

BACKGROUND

Functional dyspepsia (FD) is a complex disorder, in which multiple mechanisms underlie symptom generation, including impaired duodenal barrier function. Moreover, an altered duodenal bile salt pool was recently discovered in patients with FD. We aimed to evaluate the relationship between bile salts, bacterial translocation, and duodenal mucosal permeability in FD.

METHODS

Duodenal biopsies from patients with FD and healthy volunteers (HV) were mounted in Ussing chambers to measure mucosal resistance and bacterial passage in the absence and presence of fluorescein-conjugated Escherichia coli and glyco-ursodeoxycholic acid (GUDCA) exposure. In parallel, duodenal fluid aspirates were collected from patients and bile salts were analyzed.

KEY RESULTS

The transepithelial electrical resistance of duodenal biopsies from patients was lower compared with HV (21.4 ± 1.3 Ω.cm² vs. 24.4 ± 1.2 Ω.cm² ; P = .02; N = 21). The ratio of glyco-cholic and glyco-chenodeoxycholic acid (GCDCA) to tauro- and GUDCA correlated positively with transepithelial electrical resistance in patients. Glyco-ursodeoxycholic acid slightly altered the mucosal resistance, resulting in similar values between patient and healthy biopsies (22.1 ± 1.0 Ω.cm² vs. 23.0 ± 1.0 Ω.cm² ; P = .5). Bacterial passage after 120 minutes was lower for patient than for healthy biopsies (0.0 [0.0-681.8] vs. 1684.0 [0.0-4773.0] E coli units; P = .02). Glyco-ursodeoxycholic acid increased bacterial passage in patient biopsies (102.1 [0.0-733.0] vs. 638.9 [280.6-2124.0] E coli units; P = .009). No correlation was found between mucosal resistance and bacterial passage.

CONCLUSIONS & INFERENCES

Patients with FD displayed decreased duodenal mucosal resistance associated with bile salts, however, not associated with bacterial passage in vitro. In addition, the hydrophilic bile salt glyco-ursodeoxycholic acid abolished differences in mucosal resistance and bacterial passage between patient and control group.

Altered duodenal bile salt concentration and receptor expression in functional dyspepsia

Background

Functional dyspepsia is a common functional gastrointestinal disorder in which a variety of pathophysiological mechanisms such as increased intestinal permeability and low-grade inflammation are involved. The factor causing these alterations, however, has not been identified.

Objective

We aimed to evaluate the luminal bile salt content and receptor expression in patients with functional dyspepsia and healthy volunteers.

Methods

Gastroduodenoscopy was performed to obtain duodenal biopsies from 25 healthy volunteers and 25 patients with functional dyspepsia (Rome III) to measure duodenal bile salt receptor expression with Western blot. Duodenal fluid aspirates were collected at fixed time points during fasted and fed state conditions and bile salt composition analysis was performed by liquid chromatography-mass spectrometry/mass spectrometry.

Results

Patients (N = 17) displayed decreased fasted bile salt concentrations compared to healthy volunteers (N = 20) over time (1.8 ± 0.3 mM vs 3.6 ± 0.5 mM; p = 0.03). In addition, an increased expression of duodenal bile salt sensor vitamin D receptor was found in patients (3.7 ± 1.0-fold; p < 0.0005; N = 24 for both groups).

Conclusion

Patients with functional dyspepsia are characterized by a decreased duodenal bile salt concentration in fasted state and an increased duodenal vitamin D receptor expression.