Effects of nVNS on Stress Reactivity in IBS (U54: nVNS RCT)

Device: Participants will self-administer a transcutaneous cervical nVNS device, Truvaga Plus, which is identical to GammaCore but is rechargeable. Truvaga Plus is classified as a general wellness product that does not require FDA clearance and can be purchased without a prescription (electroCore LLC, Basking Ridge, NJ, USA, letter of support).

Usage: The nVNS will be delivered via two stainless steel contact surfaces that are coated with conductive gel before each treatment. The device will be positioned in parallel with the carotid pulse on the left side of the neck. Two back-to-back 2-minute nVNS stimulations (4 minutes total) will be administered twice daily at home for 8 weeks.

Intensity: Level is dependent on the patient. They will be instructed to increase the intensity until they feel a strong but comfortable sensation-tingling or a slight lip pull is common. Most users find the ideal intensity between levels 4 and Frequency: 2 sessions, 2x daily; 224 sessions total

Self-administered transcutaneous cervical nVNS device

Participants assigned to the Usual Care arm will undergo the same assessments as those in the nVNS arm but will not receive any specific intervention from the project. No restrictions will be placed on participants, except that they will be asked not to start any new therapies for IBS or any new medicines unless deemed necessary by their healthcare provider.

The IBS-SSS questionnaire is a validated measure of IBS symptom severity and has been shown to be responsive to treatment. The IBS-SSS assesses the severity of abdominal pain, frequency of abdominal pain, severity of abdominal distention, dissatisfaction with bowel habits, and interference of IBS with daily life over a 10-day period. Each of the five categories will receive a score from 0-100, and the total IBSSSS is calculated by taking the sum of these categories (range 0-500, 0 - no symptoms, 500 - very severe symptoms).

The PHQ-15 is a widely used measure of widespread somatic symptoms over 1 month that is sensitive to treatment effects. The PHQ-15 assess 15 different somatic symptoms (back pain, stomach pain, headaches, chest pain, trouble sleeping, etc.) rated by 0 - not bothered at all to 3 - bothered a lot. The scale is scored as follows: 0-4: Minimal somatic symptom severity, 5-9: Low somatic symptom severity, 10-14: Medium somatic symptom severity, 15-30: High somatic symptom severity.

SR-related brain phenotypes will be derived from prespecified MRI measures of brain structure, functional connectivity, and brain activity. MRI data will be collected at baseline and Week 8. The primary imaging analysis will compare baseline-to-Week-8 change in prespecified SR-related brain phenotypes between nVNS and Usual Care.

The proportion of participants with IBS who experience a ≥50-point reduction in IBS-SSS score from baseline will be compared between treatment groups. A reduction of at least 50 points represents a clinically meaningful improvement in IBS symptoms. The IBS-SSS questionnaire is a validated measure of IBS symptom severity and has been shown to be responsive to treatment. The IBS-SSS assesses the severity of abdominal pain, frequency of abdominal pain, severity of abdominal distention, dissatisfaction with bowel habits, and interference of IBS with daily life over a 10-day period. Each of the five categories will receive a score from 0-100, and the total IBSSSS is calculated by taking the sum of these categories (range 0-500, 0 - no symptoms, 500 - very severe symptoms).

Changes in the sympathetic nervous system (SNS)-immune gene expression profile will be evaluated as a peripheral biologic measure of stress reactivity. Whole-blood SNS-immune gene expression will be measured using mRNA-targeted sequencing. Total RNA will be isolated from whole blood, converted to cDNA using Lexogen QuantSeq 3' FWD, sequenced using Illumina sequencing, mapped to the GRCh38 reference human transcriptome using STAR, and quantified as gene-specific reads per million mapped reads. Baseline-to-Week-8 changes will be compared between nVNS and Usual Care and examined in relation to clinical symptom change. Moderator analyses will also test whether baseline SNS-immune gene expression modifies the treatment response using an SNS-immune measure-by-treatment-by-time interaction.

HRV will be evaluated as a peripheral autonomic measure of stress reactivity and compared over the treatment period. HRV will be derived from physiologic data collected using a Fitbit equipped with photoplethysmography sensors that estimate heart rate and intervals between successive beats. Participants will wear the device from baseline through the post-intervention assessment, including during sleep, to characterize longitudinal and circadian HRV. Changes in HRV will be compared between nVNS and Usual Care and correlated with symptom change. Moderator analyses will additionally test whether baseline HRV modifies treatment response through an HRV-by-treatment-by-time interaction.

Changes in the fecal microbial stress index will be evaluated as a peripheral biologic measure of stress reactivity. The fecal microbial stress index will be derived from stool samples collected at baseline and Week 8 using shotgun metagenomic sequencing. Microbial sequencing data will undergo species-level taxonomic and functional characterization. Baseline-to-Week-8 changes in the microbial stress index will be compared between nVNS and Usual Care and correlated with clinical symptom change.

Changes in the fecal metabolite stress index will be evaluated as a peripheral biologic measure of stress reactivity. The fecal metabolite stress index will be derived from stool metabolomic data obtained using LC-MS/MS-based profiling. Baseline-to-Week-8 changes in the metabolite stress index will be compared between nVNS and Usual Care and correlated with clinical symptom change. Moderator analyses will additionally test whether the baseline metabolite stress index modifies treatment response through a metabolite stress index-by-treatment-by-time interaction.

Examine associations between changes in scores on the SR-related brain phenotype signatures and changes in IBS severity, comorbid symptom scores, and peripheral biologic measures of SR. General linear models will examine associations between baseline-to-Week-8 changes in SR-related brain phenotype signature scores and corresponding changes in IBS-SSS, PHQ-15, HRV, SNS-immune gene expression, and microbial and metabolite stress indices, with adjustment for relevant covariates. Alternative approaches may be used to examine multivariate associations between changes in symptom severity, stress reactivity, comorbidity, and brain connectivity.

Predict response (Pre-Post change in extraintestinal symptoms) in nVNS compared to Usual Care. General linear model-based moderator analyses will evaluate whether baseline SR-related brain phenotype scores predict pre- to post-treatment change in extraintestinal symptom severity differently in participants assigned to nVNS versus Usual Care. Models will include baseline SR brain phenotype score, treatment group, the brain phenotype-by-treatment interaction, and prespecified covariates. A significant interaction will indicate differential prediction of treatment response.

Examine whether females with IBS with higher comorbid symptom scores will present with greater changes in SR-related brain signatures following the nVNS intervention compared to male IBS. Exploratory models will examine whether females with IBS with greater baseline comorbid symptom burden demonstrate greater baseline-to-Week-8 changes in SR-related brain signatures following nVNS compared with males with IBS. The moderator analysis includes the comorbid symptom score-by-group interaction, with adjustment for age, BMI, and diet.