Introduction

Disruptions in tight junction (TJ) protein expression leading to duodenal epithelial barrier impairment may contribute to increased intestinal permeability, potentially playing a role in functional dyspepsia (FD) pathophysiology. Currently published studies evaluated the role of several TJ proteins in FD patients with inconsistent results. Therefore, we conducted this systematic review and meta-analysis to evaluate the duodenal mucosal expression of several TJ proteins in FD.

Aims & Methods

We performed a systematic electronic search on PubMed, EMBASE, and Scopus using predefined keywords. Diagnosis of FD by ROME III or ROME IV criteria was considered acceptable. Full articles satisfying our inclusion and exclusion criteria were included. The principal summary outcome was the mean difference (MD) of several TJ proteins in FD patients and control subjects. The study aimed to find if patients diagnosed with functional dyspepsia have lower gene expression of intestinal TJ proteins compared to healthy subjects.

Results

A total of 8 and 5 studies were included in our qualitative and quantitative synthesis, respectively, with a total population of 666 participants, out of which 420 were FD patients. No significant differences were observed between FD patients and controls in the expression of claudin-1 (-0.102 [CI 95% -0.303,0.099]), claudin-2 (0.161 [CI 95% -0.134,0.456)], claudin-3 (0.278 (CI 95% -0.280,0.837]), claudin-4 (0.045 [CI 95% -0.264,0.354]), ZO-1 (-0.221[CI 95% -0.683, 0.241]), ZO-2 (-0.070 [CI 95% -0.147,0.007]), ZO-3(-0.129 [CI 95% -0.376, 0.118]), B-catenin (-0.135 [CI 95% -0.484,0.214]), E-cadherin (-0.083 [CI 95% -0.229,0.063]), and occludin (-0.158 [CI 95% -0.409, 0.093]).

Conclusion

The expressions of all evaluated proteins including claudin-1, claudin-2, claudin-3, claudin-4, ZO-1, ZO-2, ZO-3, B-catenin, E-cadherin, and occludin did not significantly differ between FD patients and controls. However, due to the limited number of included studies, results should be interpreted with caution.

Introduction

Functional dyspepsia (FD) is a common yet complex gastrointestinal disorder, characterised by postprandial fullness, early satiety, epigastric pain, and burning. With growing evidence linking diet to inflammation and symptoms, our objective was to review the evidence for the impact of dietary factors on FD symptomatology.

Aims & Methods

A systematic review was conducted to identify dietary components influencing FD symptoms in adults. Databases searched included MEDLINE, EMBASE, PsycINFO, Scopus, and Cochrane, covering January 2000 to December 2024. A total of 14 studies met eligibility criteria, with findings synthesised through narrative analysis.

Results

The search strategy yielded 18,424 articles, of which 14 met the inclusion criteria. Analysis identified seven key dietary components associated with FD: (1) a low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diet significantly improved symptoms (p = 0.04), while gluten intake was linked to early satiety (p = 0.03); (2) probiotics or prebiotics provided symptom relief (RR 1.15, p = 0.52), with probiotics alone showing a trend toward improved FD scores (RR 1.35, p = 0.061); (3) capsaicin significantly exacerbated symptoms (p < 0.001), and spicy foods were associated with increased gastric fullness (p = 0.001); (4) both peppermint-caraway oil (p < 0.00001) and cinnamon oil (p < 0.001) demonstrated significant symptom relief; (5) ginseng-based herbal porridge led to a higher rate of epigastric symptom remission by day 90 compared to placebo (45.71% vs. 20.69%, p = 0.036), while the STW 5-II formulation (a nine-herb extract) also yielded significant improvement (p = 0.008); (6) prokinetic agents reduced symptom severity (RR 0.81, p < 0.0001), while amitriptyline outperformed both placebo (40%) and escitalopram (38%), relieving symptoms in 53% of patients—particularly those with ulcer-like FD; and (7) ginger/artichoke capsules improved symptoms within 14 days (p = 0.017), while ginger/perilla tablets offered progressive relief over one to two weeks (p < 0.05 and p < 0.01, respectively). Study quality was assessed using ROBIS, RoB 2.0, and ROBINS-I tools. Of the included studies, three were rated as low risk of bias, eight as moderate, and three as serious. Despite adherence to a standardised PRISMA-based search strategy, variability in outcome reporting limited direct comparability across studies.

Table 1

Conclusion

This review highlights dietary interventions as a promising strategy for managing FD. Our findings show that specific dietary components can be implicated in inducing inflammation and symptoms in FD. Since the symptoms are related to inflammation, we propose using “inflammatory dyspepsia” to represent the true presentation of this form of dyspepsia. Large-scale randomised trials are needed to confirm findings and refine dietary guidelines.

Introduction

Functional dyspepsia (FD) is a chronic gastrointestinal disorder characterised by meal-related symptoms, which a subset of patients attribute to the consumption of gluten-containing foods [1]. Recent evidence suggests that subtle duodenal immune activation is a feature of FD, as evidenced by elevated eosinophils [2] and impaired epithelial barrier function [3]. FD patients also exhibit an altered duodenal mucosa-associated microbiota (d-MAM) when compared to controls [4]. Given the microbiome’s involvement in the digestion of gluten, we hypothesised that the d-MAM determines the capacity for gluten to disrupt the epithelium and drive immune responses in FD patients.

Aims & Methods

Duodenal biopsies were collected from 10 FD patients and 7 asymptomatic controls. The d-MAM was cultured from biopsies in a habitat simulating media [5] containing 1% wheat-gluten, for up to 48hrs. Microbial cell pellets were frozen for future microbiome sequencing and the cell-free supernatants, containing d-MAM-digested gluten, were collected. Caco2 cells were challenged with the d-MAM-digested gluten, in a Transwell model of the intestinal epithelium (n=3, 2 technical replicates). Transepithelial electrical resistance (TEER) and protein expression of markers of epithelial integrity were measured in Caco2 cells and compared between treatments. Peripheral blood mononuclear cells (PBMCs) from FD patients (n=20) and controls (n=20) were stimulated with pooled samples of FD or control d-MAM-digested gluten, or left untreated, for 44 hours. For comparison to host enzymatic breakdown of gluten, matched PBMCs were also treated with α-chymotrypsin digested, deaminated gluten (CT gluten). The T cell phenotype and presence of activation-induced markers was assessed in PBMCs by flow cytometry.

Results

Challenge of Caco2 cells with gluten digested by the FD d-MAM resulted in a significant increase in Zonula occludens-1 (p=0.007), and reduction in Myd88 (p=0.03), compared to Caco2 cells challenged with control d-MAM-digested gluten. However, TEER readings were not altered between treatment groups in Caco2 experiments. In PBMC experiments, in response to stimulation with FD or control d-MAM-digested gluten, both FD and control PBMCs exhibited heightened expression of activation markers (CD4⁺OX40⁺CD25⁺), when compared to their respective unstimulated cells (p<0.05). When assessing the T-cell phenotype we observed that FD d-MAM-digested gluten promoted an increase in T-helper (Th) 2 cells in both FD (p=0.007) and control (p=0.0001) PBMCs. Meanwhile, control d-MAM-digested gluten stimulation resulted in elevated Th17.1 cells in FD (p<0.0001) and control (p=0.02) PBMCs, when compared to unstimulated cells. Alternatively, CT gluten stimulation did not alter any of the assessed lymphocyte populations in FD or control PBMCs when compared to unstimulated cells, suggesting host digestion of gluten isn’t sufficient to induce immune responses in FD.

Conclusion

Our findings suggest that the d-MAM of FD patients digest gluten in a way that promotes epithelial barrier remodelling and altered immune responses compared to the d-MAM from asymptomatic individuals. The promotion of a Th2 T-cell phenotype by the FD d-MAM is consistent with reports of increased Th2-associated cells, such as eosinophils, in FD patients [6]. These results highlight the likely role of microbiome-gluten interactions in FD, indicating the potential for novel dietary therapies and microbial approaches to management.

References

1. Potter, M., et al., Incidence and prevalence of self-reported non-coeliac wheat sensitivity and gluten avoidance in Australia. Med J Aust, 2020. 212(3): p. 126-131.
2. Shah, A., et al., Duodenal Eosinophils and Mast Cells in Functional Dyspepsia: A Systematic Review and Meta-Analysis of Case-Control Studies. Clinical Gastroenterology and Hepatology, 2022. 20(10): p. 2229-2242.e29.
3. Puthanmadhom Narayanan, S., et al., Duodenal Mucosal Barrier in Functional Dyspepsia. Clin Gastroenterol Hepatol, 2022. 20(5): p. 1019-1028.e3.
4. Shanahan, E.R., et al., Alterations to the duodenal microbiota are linked to gastric emptying and symptoms in functional dyspepsia. Gut, 2023. 72(5): p. 929-938.
5. Schooth, L., Defining the Role of the Mucosa-Associated Microbiota in Digestive Health and Disease Using Novel ex-vivo Combinations of Microbe Culture with Metagenomics. 2024 [Doctoral thesis, The University of Queensland], UQ eSpace.
6. Burns, G.L., et al., Type 2 and type 17 effector cells are increased in the duodenal mucosa but not peripheral blood of patients with functional dyspepsia. Front Immunol, 2022. 13: p. 1051632.

Disclosure

JP, EH, CN, SS, SR, MS, KH, GB, and KD have no disclosures to report.
NT: Financial support from: BluMaiden (microbiome advisory board) (2021), Comvita Mānuka Honey (2021) (digestive health), Biocodex (functional dyspepsia tool), Microba (microbiome advisory board) outside the submitted work. In addition, Dr. Talley has a patent Nepean Dyspepsia Index (NDI) 1998, Biomarkers of IBS licensed, a patent Licensing Questionnaires Talley Bowel Disease Questionnaire licensed to Mayo/Talley, a patent issued, “Diagnostic marker for functional gastrointestinal disorders” Australian Patent Application WO2022256861A1via the University of Newcastle and UniQuest (University of Queensland) and ”Methods and compositions for treating age-related neurodegenerative disease associated with dysbiosis” US Application No. 63/537,725. Dr. Talley is supported by funding from the National Health and Medical Research Council (NHMRC) to the Centre for Research Excellence in Digestive Health and he holds an NHMRC Investigator grant.
SK: Grants from National Health and Medical Research Council (Ideas Grant and Centre for Research Excellence), grants from Viscera Labs (Research contract), grants from Microba Life Science (Research contract), personal fees from Gossamer Bio, personal fees from Anatara Lifescience, personal fees from Immuron, personal fees from Microba Life Science.

Introduction

Functional dyspepsia (FD) is a common gastrointestinal disorder with limited treatment options. Itopride, a compound that combines dopamine D2 receptor antagonism with inhibition of acetylcholinesterase, may offer benefits over other prokinetics.

Aims & Methods

This meta-analysis evaluates the therapeutic efficacy of Itopride compared to placebo and other prokinetic agents in managing FD symptoms.
A total of 19 randomized controlled trials were included in the analysis, comprising six placebo-controlled studies (n=1981, 976 on placebo and 1005 on Itopride) and 13 trials comparing Itopride to another prokinetic (n=1077, 515 on Itopride and 562 on control prokinetics including mosapride citrate, levosulpiride, metoclopramide, domperidone, and cisapride). Meta-analyses were conducted using a random-effects (DerSimonian and Laird) model. Outcome measures included overall responder rate and symptom assessment, comparing Itopride to 1) all prokinetics and 2) placebo. In addition, Itopride was compared to placebo and domperidone for symptom scores of epigastric pain and early satiation. Results are presented as Cohen’s d (95% CI) or odds ratios(OR) (95% CI).

Results

Analysis of responder rates from seven placebo-controlled and nine active comparator studies showed a statistically significant benefit of Itopride over placebo (OR=1.25, 1.07 to 1.45, p=0.01), with no significant difference when compared to other prokinetics (OR=1.11, 0.93 to 1.34).
When assessing overall symptom scores, three placebo-controlled and four prokinetic-controlled trials were analyzed. Itopride showed a moderate effect size compared to other prokinetics (Cohen’s d=0.51, 0.13 to 0.88, p=0.01) and a large but not statistically significant effect compared to placebo (Cohen’s d=1.14, -0.43 to 2.71).
Early satiation was assessed in six domperidone-controlled trials, yielding a significant odds ratio of 1.37 (1.02 to 2.67, p=0.04). A large but not statistically significant difference was found compared to placebo (two trials, Cohen’s d=1.10, -0.47 to 2.67). For epigastric pain, a moderate but not statistically significant difference was found with placebo (two trials, Cohen’s d=0.68, -0.01 to 1.38) or domperidone (four trials, OR=0.85, 0.63 to 1.16).

Conclusion

This meta-analysis suggests that Itopride provides significant symptom relief in patients with FD compared to placebo, particularly in overall responder rates. While Itopride’s benefits over other prokinetics were modest in general symptom relief, it demonstrated a statistically significant advantage over domperidone for early satiation.

Introduction

Functional dyspepsia (FD) is one of the most frequent disorders of gut-brain interaction, but according to the recent UEG consensus there is a lack of effective treatment options.(1) An important role for duodenal immune activation and increased mucosal permeability has been implied in the pathophysiology of FD. In a recent in vitro study on duodenal biopsies from FD patients palmitoylethanolamide (PEA), an endogenously produced anti-inflammatory compound, was shown to stabilize acid-induced activation of mast cells.(2) PEA is produced in several cell types and tissues to counteract inflammatory and other noxious responses, and diminished levels have been reported in duodenal biopsies from FD patients.(2)

Aims & Methods

In this randomized double blind placebo-controlled trial, we aimed to evaluate the effect of PEA supplementation on symptoms, mucosal integrity and duodenal low grade inflammation. After a 2-week run-in, patients were randomized to placebo or PEA 400 mg t.i.d. for 8 weeks. Before and after the treatment phase, patients underwent upper gastrointestinal endoscopy with biopsies and a ¹³C-octanoic acid gastric emptying breath test to measure gastric emptying half time (GE T_1/2). Biopsies were used to measure transepithelial electrical resistance (TEER) and paracellular flux of 4kDa-fluorescein labelled dextran (FITC D4) in Ussing chambers and to count mast cells. Symptoms were recorded using the patient assessment of upper gastrointestinal symptom severity index (PAGI-SYM) and Leuven Postprandial Distress Scale (LPDS). The primary endpoint was the improvement in LPDS score. Symptoms and pathophysiological parameters were compared between PEA and placebo after 8 weeks of treatment.

Results

In this study, 61 patients were included of which 33 were assigned to placebo and 28 to PEA. The baseline characteristics are shown in Table 1. After treatment, no significant differences were found between the PEA and placebo group regarding LPDS scores (1.5±0.2 vs. 1.3±(0.2), p=0.47), GE T_1/2 (83 (76-98) vs. 95 (72-109) min, p=0.57), TEER (27.3±0.8 vs. 28.0±1.0 Ω * cm², p=0.21), and duodenal mast cell counts (589±43 vs. 557±34 mast cells / mm², p=0.56). FITC D4 flux tended to be lower after PEA (27.9±1.9 vs. 33.3±2.2 pmol, p=0.06), with a more robust effect in patients taking a proton pump inhibitor (Δ FITC D4 flux -3.8±3.4 vs. 7.2±2.8 pmol, p=0.027). In patients that received PEA, the Δ FITC D4 flux correlated negatively with the Δ total PAGI-SYM score (r -0.49, p=0.02) and Δ of mast cell counts correlated positively with Δ PAGI-SYM fullness subscale (r=0.49, p=0.04).

Conclusion

In FD, PEA does not improve gastrointestinal symptoms but improves duodenal barrier function mainly in patients that are taking a PPI. The interaction between PEA and PPI and its relevance for disorders of gut-brain interaction deserves further study.

References

1: Wauters L, Dickman R, Drug V, Mulak A, Serra J, Enck P, Tack J; ESNM FD Consensus Group; Accarino A, Barbara G, Bor S, Coffin B, Corsetti M, De Schepper H, Dumitrascu D, Farmer A, Gourcerol G, Hauser G, Hausken T, Karamanolis G, Keszthelyi D, Malagelada C, Milosavljevic T, Muris J, O'Morain C, Papathanasopoulos A, Pohl D, Rumyantseva D, Sarnelli G, Savarino E, Schol J, Sheptulin A, Smet A, Stengel A, Storonova O, Storr M, Törnblom H, Vanuytsel T, Velosa M, Waluga M, Zarate N, Zerbib F. United European Gastroenterology (UEG) and European Society for Neurogastroenterology and Motility (ESNM) consensus on functional dyspepsia. United European Gastroenterol J. 2021 Apr;9(3):307-331. doi: 10.1002/ueg2.12061. PMID: 33939891; PMCID: PMC8259261.
2: Sarnelli G, Pesce M, Seguella L, Lu J, Efficie E, Tack J, Elisa De Palma FD, D'Alessandro A, Esposito G. Impaired Duodenal Palmitoylethanolamide Release Underlies Acid-Induced Mast Cell Activation in Functional Dyspepsia. Cell Mol Gastroenterol Hepatol. 2021;11(3):841-855. doi: 10.1016/j.jcmgh.2020.10.001. Epub 2020 Oct 14. PMID: 33065341; PMCID: PMC7858681.

Introduction

Duodenal immune activation including increased eosinophil and mast cell infiltration have previously been reported in functional dyspepsia (FD). However, detailed insights in the nature of this immune activation are lacking, as previous research focused on routine histological investigation¹.

Aims & Methods

We aimed to characterise duodenal innate immune cell populations in FD and investigate eosinophilic mediator release. Furthermore, we aimed to evaluate the potential anti-inflammatory effects of a high-dose proton pump inhibitor (PPI) course in FD. Patients with FD (Rome IV) and healthy controls (HC) were recruited to undergo upper GI endoscopy with duodenal biopsies, which was repeated in FD after 4 weeks of high-dose PPI (pantoprazole 40mg bid). Lamina propria leukocytes were isolated from fresh biopsies and stained with fluorescently labelled antibodies for subsequent flow cytometric analysis using an LSR Fortessa flow cytometer (BD). Leukocytes were gated as CD45⁺ cells within single viable (FVD780^-) cells. Within this population, eosinophils (Siglec8⁺, CD117^-, CD193⁺, SSC^high), mast cells (Siglec8⁺, CD117⁺) and neutrophils (CD16⁺, SSC^high) were expressed as percentage of leukocytes. Faecal samples were obtained from all participants and proteins were extracted². Eosinophil derived neurotoxin (EDN) was measured in duodenal biopsy supernatants and faecal protein extracts using ELISA (Diagnostics Development). Data were analysed in Prism by (non-)parametric tests depending on normality and calculation of Spearman’s correlation r.

Results

Data are available from 22 FD patients (18 female, mean ± SEM age 33 ± 3 years) and 27 HC (21 female, 29 ± 2 years). Duodenal leukocytes, eosinophils, mast cells and neutrophils were not different between patients and controls (Table). However, duodenal leukocyte proportions decreased in FD after PPI, with an opposite effect for mast cells. Duodenal eosinophil and neutrophil proportions remained unchanged after PPI. EDN released by duodenal biopsies was similar in FD and HC, without changes after PPI (Table). Similarly, no between- or within-group differences were found for faecal EDN. Eosinophil proportions in FD at both visits were significantly associated with EDN release from biopsies (r=0.61, p=0.001), but not faecal EDN (r=0.004, p=0.98). In contrast, faecal (r=0.44, p=0.03) but not supernatant EDN (r=0.33, p=0.1) was linked to duodenal eosinophils in controls.

Table: Between- (FD vs HC) and within-group (FD vs FD+PPI) comparisons.

Conclusion

Using flow cytometric evaluation of the duodenal mucosa, we found similar proportions of innate immune cells, including eosinophils and mast cells in FD patients compared to controls. However, immunomodulatory effects of a high-dose PPI course in FD included reduced leukocyte proportions and increased mast cells. A strong association between duodenal release of EDN and eosinophil numbers in patients but not controls, suggests altered eosinophil degranulation in FD, which warrants further investigation. Finally, faecal EDN levels were only linked to duodenal eosinophils in controls but not patients, limiting its suitability as a biomarker.

References

¹ Ceulemans et al. Front Neurosci 2022
² Peterson et al. Am J Gastro 2002