Grover, Madhusudan

Background Irritable bowel syndrome (IBS) is a complex disorder of gut-brain interaction, with heterogeneous symptoms, no available biomarkers and limited pathogenetic insight. Objective To identify genetic risk factors and actionable mechanisms for future clinical translation in IBS. Design We conducted a genome-wide association study (GWAS) meta-analysis of IBS in 2 775 539 individuals from 22 biobanks. IBS genetics was studied across multiple ancestries, different case definitions and symptom-related subtypes. Heritability and genetic correlations with other traits were estimated, and Mendelian randomisation was used to test causal relationships. GWAS data were functionally annotated and fine-mapped to prioritise tissues, cell types, pathways, candidate genes, specific mechanisms and druggable targets. Results Significant heritability was only detected in individuals of European ancestry, with near-identical genetic architecture across case definitions. Genetic correlations with GI, psychiatric and cardiometabolic traits were observed, including causal relationships with triglyceride (TG) levels. Functional annotation of IBS risk loci highlighted cell types and pathways relevant to brain, enteric neuro-glial and cardiometabolic domains, as well as actionable targets like GCKR, a regulator of TG metabolism. Druggability analyses converged on cardiometabolic mechanisms, including TG modulation. IBS polygenic risk scores were derived and showed a significant association with case status in an independent case-control dataset, supporting further evaluation in external population-based and clinically ascertained cohorts. Conclusions This study provides the most comprehensive assessment of IBS genetics to date, demonstrating reproducible polygenic inheritance. We link IBS risk to convergent neurogastrointestinal and novel cardiometabolic mechanisms, highlight specific biological pathways and actionable mechanisms and outline translational opportunities emerging from integrated computational analyses.

Abstract Interstitial cells of Cajal (ICC) regulate gastrointestinal motility by generating electrical slow waves that orchestrate downstream calcium (Ca 2 + ) waves and coordinate smooth muscle contractions. A reduced ICC number has been reported in diabetic gastroparesis patients and in mouse models of delayed gastric emptying (DGE). However, functional changes in ICC propagating across the gastric regions in intact stomach are not well understood. The aim of this study was to develop an imaging approach to visualize ICC Ca 2+ waves in mouse stomach and determine spatiotemporal changes in mice with DGE. Tamoxifen‐treated B6.GCaMP5‐KitCreERT2 female mice were used as non‐diabetic controls (Non‐Db), while mice treated with streptozocin to induce diabetes were categorized as having normal (Db‐NGE) or delayed (Db‐DGE) gastric emptying based on emptying of solids. The ICC Ca 2+ network was imaged from excised intact mouse stomachs and subsequently opened along the lesser curvature and pinned flat. ICC Ca 2+ waves typically propagated along the greater curvature from the fundus–corpus line toward the antrum. The propagation length of ICC Ca 2+ activity was significantly decreased in Db‐DGE compared to Non‐Db and Db‐NGE and correlated to longer GE times. There was also a decrease in frequency, and the velocity was significantly faster in stomachs from Db‐DGE compared to Non‐Db and Db‐NGE. All experimental groups exhibited similar proportions of aberrant Ca 2+ propagation patterns (e.g., retrograde waves), but ectopic initiation only occurred in Db‐DGE stomachs. Thus, DGE is possibly driven by dysfunction in Ca 2+ activity in the ICC network that propagates rapidly over short distances, resulting in uncoordinated, non‐phasic muscle activity. image Key points Dysfunction of the interstitial cells of Cajal (ICC) has been implicated in diabetic gastroparesis but the changes in spatiotemporal properties of ICC network activity are not known. We developed an ex vivo Ca 2+ imaging approach to visualize ICC network activity across the entire stomach and determined changes in ICC Ca 2+ activity in a diabetic mouse model of delayed gastric emptying (GE). Decreased frequency and increased velocity of ICC Ca 2+ activity was observed in stomachs of diabetic mice with delayed GE. Ectopic initiation was a key feature associated with delayed GE. The propagation length of ICC Ca 2+ activity was inversely correlated to GE times and significantly reduced in stomach preparations from diabetic mice with delayed GE.

INTRODUCTION: Bloating, distention, and gas-related gastrointestinal (GI) symptoms are frequently reported by patients across the spectrum of disorders of gut-brain interaction (DGBI). We aimed to characterize these using latent class modeling in a large multinational survey. METHODS: A nationwide survey of adults in the United States, United Kingdom, and Mexico used quota sampling for demographic balance. It included Rome IV diagnostic questions, Intestinal Gas Questionnaire, Patient Health Questionnaires for anxiety and depression (PHQ-4) and somatization (PHQ-12), quality of life (PROMIS Global-10), and lifestyle questions. Latent class analysis was performed using “depmix” in RStudio 4.2.3. RESULTS: A total of 3,471 subjects experiencing bloating and/or distention (mean age 43 years, 57% female) were included. Using 42 demographic and pertinent clinical variables, latent class analysis revealed 6 distinct clusters. The first 2 clusters demonstrated limited-to-moderate impairment in health-related quality of life (HRQoL), with both characterized by some degree of dietary and supplement associations; however, cluster 2 lacked specific triggers observed in other clusters. The subsequent 2 clusters showed favorable HRQoL and mild gas-related symptoms, with only cluster 4 exhibiting distinct dietary triggers. The final 2 clusters, associated with bowel dysfunction, showed a higher prevalence of irritable bowel syndrome (IBS) with constipation and IBS mixed in cluster 5, and IBS with diarrhea in cluster 6. These bowel dysfunction clusters exhibited severe gas symptoms in the preceding 24 hours and greater HRQoL impairment compared with the other 4 clusters. Notably, cluster 5 was linked to dietary triggers, whereas cluster 6 was defined by psychosocial comorbidities. DISCUSSION: Bloating and distention patients are likely driven by variable influences of dietary, psychological, and bowel dysfunction. Further studies are needed to identify mechanisms and titrate treatment suited to specific mechanistic drivers.

Using 32 immune cell surface markers, we identified 23 monocyte clusters in murine blood. Diabetic gastroparesis was associated with a significant decrease in two circulating classical monocyte-like clusters and an upregulation of the Ccr2-Ccl2 axis in the gastric muscularis propria, suggesting increased tissue monocyte migration. This study offers new targets by pointing to a possible role for two classical monocyte subsets connected to the Ccr2- Ccl2 axis.

AbstractBackgroundGastroparesis (GP) is characterized by delayed gastric emptying in the absence of mechanical obstruction.ObjectiveGenetic predisposition may play a role; however, investigation at the genome‐wide level has not been performed.MethodsWe carried out a genome‐wide association study (GWAS) meta‐analysis on (i) 478 GP patients from the National Institute of Diabetes and Digestive and Kidney Diseases Gastroparesis Clinical Research Consortium (GpCRC) compared to 9931 population‐based controls from the University of Michigan Health and Retirement Study; and (ii) 402 GP cases compared to 48,340 non‐gastroparesis controls from the Michigan Genomics Initiative. Associations for 5,811,784 high‐quality SNPs were tested on a total of 880 GP patients and 58,271 controls, using logistic mixed models adjusted for age, sex, and principal components. Gene mapping was obtained based on genomic position and expression quantitative trait loci, and a gene‐set network enrichment analysis was performed. Genetic associations with clinical data were tested in GpCRC patients. Protein expression of selected candidate genes was determined in full thickness gastric biopsies from GpCRC patients and controls.ResultsWhile no SNP associations were detected at strict significance (p ≤ 5 × 10−8), nine independent genomic loci were associated at suggestive significance (p ≤ 1 × 10−5), with the strongest signal (rs9273363, odds ratio = 1.4, p = 1 × 10−7) mapped to the human leukocyte antigen region. Computational annotation of suggestive risk loci identified 14 protein‐coding candidate genes. Gene‐set network enrichment analysis revealed pathways potentially involved in immune and motor dysregulation (pFDR ≤ 0.05). The GP risk allele rs6984536A (Peroxidasin‐Like; PXDNL) was associated with increased abdominal pain severity scores (Beta = 0.13, p = 0.03). Gastric muscularis expression of PXDNL also positively correlated with abdominal pain in GP patients (r = 0.8, p = 0.02). Dickkopf WNT Signaling Pathway Inhibitor 1 showed decreased expression in diabetic GP patients (p = 0.005 vs. controls).ConclusionWe report preliminary GWAS findings for GP, which highlight candidate genes and pathways related to immune and sensory‐motor dysregulation. Larger studies are needed to validate and expand these findings in independent datasets.

Summary Background Patients with gastroparesis and related disorders have symptoms including early satiety, postprandial fullness and bloating. Buspirone, a 5‐HT 1 receptor agonist, may improve fundic accommodation. Aim To determine if buspirone treatment improves early satiety and postprandial fullness in patients with symptoms of gastroparesis. Methods This 4‐week multi‐centre clinical trial randomised patients with symptoms of gastroparesis and moderate‐to‐severe symptoms of fullness (Gastroparesis Cardinal Symptom Index [GCSI] early satiety/postprandial fullness subscore [ES/PPF]) to buspirone (10 mg orally) or placebo three times per day. The primary outcome was a change in the ES/PPF from baseline to 4 weeks. The primary analysis was per protocol intention‐to‐treat ANCOVA of between‐group baseline vs. 4‐week differences (DoD) in ES/PPF adjusted for baseline ES/PPF. Results are reported using both nominal and Bonferroni (BF) p values. Results and conclusions Ninety‐six patients (47 buspirone, 49 placeboes; 92% female, 50% delayed gastric emptying, 39% diabetic) were enrolled. There was no between‐groups difference in the 4‐week ES/PPF primary outcome: −1.16 ± 1.25 (SD) on buspirone vs −1.03 ± 1.29 (SD) on placebo (mean DoD: −0.11 [95% CI: −0.68, 0.45]; p = 0.69). Buspirone performed better than placebo in patients with severe‐to‐very severe bloating at baseline compared to patients with none to moderate: (ES/PPF DoD = −0.65 vs. 1.58, p TX*GROUP = 0.003; p BF = 0.07). Among individual GCSI symptoms, only bloating appeared to improve with buspirone vs. placebo. Conclusions Patients with moderate‐to‐severe early satiety/postprandial fullness and other symptoms of gastroparesis did not benefit from buspirone treatment to improve the ES/PPF primary outcome compared with placebo. There was a suggestion of the benefit of buspirone in patients with more severe bloating. Trial Registration: ClinicalTrials.gov NCT0358714285.

AbstractBackgroundAutoimmunity may play a role in the pathogenesis of gastroparesis in a subset of patients. Antinuclear antibody (ANA) testing is often used to screen for autoimmune disorders.Aims1) Determine prevalence of a positive ANA in patients with gastroparesis; 2) Describe characteristics of idiopathic gastroparesis patients with positive ANA.MethodsPatients were assessed with gastric emptying scintigraphy (GES), symptom assessment via Patient Assessment of Upper GI Symptoms [PAGI‐SYM], and blood tests—ANA, erythrocyte sedimentation rate (ESR), C‐reactive protein (CRP).ResultsPositive ANA was seen in 148 of 893 (17%) patients with gastroparesis, being similar in idiopathic (16% of 536 patients), T1DM (16% of 162), T2DM (18% of 147), and postfundoplication (19% of 48 patients) gastroparesis. Among 536 patients with idiopathic gastroparesis, ANA titer 1:40–1:80 was seen in 33 (6%) patients, 1:160–1:320 in 36 (7%) patients, and ≥1:640 in 17 (3%) patients. Increasing ANA titer was associated with female gender (p = 0.05), Hispanic ethnicity (p = 0.02), comorbid rheumatoid arthritis (p = 0.02), systemic sclerosis (p = 0.004), and elevated ESR (p = 0.007). ANA positivity was associated with lower total GCSI (p = 0.007) and lower nausea/vomiting subscale (p = 0.0005), but not related to gastric emptying.ConclusionsThe prevalence of a positive ANA in patients with gastroparesis was high at ~17% and did not differ significantly based on etiology. In idiopathic patients, ANA positivity was associated with rheumatoid arthritis, systemic sclerosis, and elevated ESR. ANA‐positive gastroparesis represents a subset who often have other autoimmune symptoms or disorders, but less severe nausea and vomiting.

Abstract Background Gastric electrical stimulation (GES) for treating gastroparesis symptoms is controversial. Methods We studied 319 idiopathic or diabetic gastroparesis symptom patients from the Gastroparesis Clinical Research Consortium (GpCRC) observational studies: 238 without GES and 81 with GES. We assessed the effects of GES using change in GCSI total score and nausea/vomiting subscales between baseline and 48 weeks. We used propensity score methods to control for imbalances in patient characteristics between comparison groups. Key Results GES patients were clinically worse (40% severe vs. 18% for non‐GES; P < .001); worse PAGI‐QOL (2.2. vs. 2.6; P = .003); and worse GCSI total scores (3.5 vs. 2.8; P < .001). We observed improvements in 48‐week GCSI total scores for GES vs. non‐GES: improvement by ≥ 1‐point (RR = 1.63; 95% CI = (1.14, 2.33); P = .01) and change from enrollment (difference = −0.5 (−0.8, −0.3); P < .001). When adjusting for patient characteristics, symptom scores were smaller and not statistically significant: improvement by ≥ 1‐point (RR = 1.29 (0.88, 1.90); P = .20) and change from the enrollment (difference = −0.3 (−0.6, 0.0); P = .07). Of the individual items, the nausea improved by ≥ 1 point (RR = 1.31 (1.03, 1.67); P = .04). Patients with GCSI score ≥ 3.0 tended to improve more than those with score < 3.0. (Adjusted P = 0.02). Conclusions and Inferences This multicenter study of gastroparesis patients found significant improvements in gastroparesis symptoms among GES patients. Accounting for imbalances in patient characteristics, only nausea remained significant. Patients with greater symptoms at baseline improved more after GES. A much larger sample of patients is needed to fully evaluate symptomatic responses and to identify patients likely to respond to GES.

Increased amino acids in the dysbiotic gut influences susceptibility to Clostridioides difficile infection in mice and humans.