EVIDENCE OF DUODENAL EPITHELIAL BARRIER IMPAIRMENT IN A RODENT MODEL OF VISCERAL HYPERALGESIA AMELIORATED BY AURICULAR VAGUS NERVE STIMULATION

Introduction: Patients with upper gastrointestinal (UGI) symptoms of abdominal pain, nausea, vomiting, and bloating often complain within the postprandial period. These symptoms overlap in gastroparesis (GP) and functional dyspepsia (FD), with the only distinction of gastric emptying delay being the main facet in clinical evaluation that separates the two entities. The small bowel postprandial response, an increase in contractile activity following meal intake, is known to be blunted in GP compared to healthy volunteers (HV) as measured by wireless motility capsule (WMC). This neuro-mediated reflex has not been evaluated in those with FD. The primary aim of the study was to assess the small bowel postprandial response in FD compared to GP and HV.
Methods: WMC data of HV and subjects with UGI symptoms suggestive of GP from prior clinical trials were analyzed. A gastric emptying time (GET) cut-off of 5 hours was used to classify symptomatic subjects as GP or FD. All subjects ingested a 250 cc standardized Ensure® meal after a 6-hour fast post-WMC ingestion. Area under the pressure curve (AUC), a measure of both contractile frequency and amplitude, data was extracted from a 20 minutes pre-prandial baseline and three consecutive 20-minute postprandial time periods to allow for granular assessment of contractility during the first 60-minute postprandial period. Comparison of postprandial windows to baseline and comparison of respective windows between subject groups was performed using a paired and unpaired t-tests, respectively. Significance level was defined as p< 0.05.
Key Results: 107 HV, 18 FD and 24 GP subjects were analyzed. All subjects showed a significant postprandial increase in AUC in all periods compared to baseline (p < 0.05). HV showed a robust meal response from meal ingestion to 40 minutes which expectedly decreases from 40 to 60 minutes postprandially (Figure 1). GP had a blunted meal response in all post-prandial time periods compared to HV (Figure 1). FD had a postprandial response pattern distinct from HV and GP, showing some intermediate blunting immediately after the meal but with distinctly increased contractile activity later compared to GP (Figure 1).
Conclusion: FD subjects have small bowel motor component abnormalities during the meal response without delayed gastric emptying. The patterns appear to be intermediate blunting (within the first 20-minutes postprandially) of the small bowel meal response in between a healthy and gastroparetic pattern. These motility abnormalities in the small bowel could be contributing to symptoms in FD or be a consequence of neuro-enteric dysfunction in FD patients.

Background and aims: Epigastric pain is one of the major symptoms in patients with functional dyspepsia (FD) that affects up to 16% of the general population. Currently treatment options for epigastric pain in FD are limited. Our previous studies have shown promising effects of auricular vagus nerve stimulation (aVNS) for treating pain in both animal model of gastric hyperalgesia (GH) and patients with FD. Duodenal epithelial barrier impairment and immune activation are believed to play an important role in the pathogenesis of FD. This study aimed to explore analgesic effects and autoimmune mechanisms of aVNS in treating visceral pain in a rodent model of GH.
Methods: GH was induced by the gastric iodoacetamide (IA) treatment in the neonatal stage. Control rats (n=5) received neonatal vehicle treatment. The IA-treated rats in adulthood were randomized to Sham (no stimulation output, n=10) or aVNS (n=10), 1 hour daily for 10 days using parameters previously shown to suppress visceral pain. Gastric visceromotor reflex to graded gastric distensions (GD) was assessed by electromyogram (EMG). Autonomic functions were assessed by the spectral analysis of heart rate variability (HRV) to derive the low frequency (LF, reflecting mainly sympathetic activity) and high frequency (HF, reflecting vagal activity) components. Duodenal tissues were collected for the assessment of mucosal barrier function by the measurement of transepithelial electrical resistance (TEER) and the measurement of tight junction protein expression using Western blot. Duodenum mast cell activity was accessed by tryptase concentration normalized with tissue weight.
Results: 1) Compared with sham-aVNS, aVNS resulted in a decrease in the EMG response to GD, at 40, 60 and 80mmHg (P<0.01 for all) and mast cell activity accessed by tryptase concentration (10.3±3.6 vs. 14.9±5.0 ug/ml/mg, P=0.05), and an increase in duodenum mucosal integrity assessed by TEER (49.6±14.1 vs. 33.2±13.5 Ω.cm², P=0.03), the expression of duodenal tight junction ligandins occludin by 4.5 fold (P=0.026) and vagal efferent activity (HF: 0.52±0.24 vs. 0.33±0.13, P<0.05; LF/HF: 1.30±1.05 vs. 2.52±1.47, P<0.05) in the IA-treated rats. 2) Moreover, the aVNS-treated GH rats showed values comparable to the normal controls in mast cell activity (10.3±3.6 vs. 10.4±2.9 ug/ml/mg, P=0.94), TEER (49.6±14.1 vs. 50.6±5.5, P=0.87), protein expression of occludin (P=0.36) and vagal activity (HF: 0.52±0.24 vs. 0.58±0.17, P=0.62; LF/HF: 1.30±1.05 vs. 0.89±0.73, P=0.41), suggesting normalization of these activities/functions.
Conclusion: aVNS ameliorates gastric hypersensitivity by improving duodenal barrier function and structure possibly mediated via the autoimmune mechanisms.