From intestinal permeability to dysmotility: the biobreeding rat as a model for functional gastrointestinal disorders

Alterations in gastrointestinal motility assessed by high-resolution antroduodenal manometry in patients with severe disorders of gut-brain interaction

Data are limited regarding gastrointestinal motility disturbance in disorders of gut-brain interaction (DGBI). This study aimed to characterize antroduodenal motor alterations in patients with high-resolution antroduodenal manometry (HR-ADM). HR-ADM was performed in patients with severe DGBI and compared with healthy volunteers (HV). HR-ADM used a commercially available probe composed of 36 electronic sensors spaced 1 cm apart and positioned across the pylorus. Antral and duodenal motor high-resolution profiles were analyzed, based on the frequency, amplitude, and contractile integral/sensor (CI/s) calculated for each phase of the migrating motor complex (MMC). Eighteen HV and 64 patients were investigated, 10 with irritable bowel syndrome (IBS), 24 with functional dyspepsia (FD), 15 with overlap IBS-FD, and 15 with other DGBI. Compared with HV, patients had a lower frequency of phase II duodenal contractions (27 vs. 51 per hour; P = 0.002) and a lower duodenal phase II contraction amplitude (70 vs. 100 mmHg; P = 0.01), resulting in a lower CI/s of phase II (833 vs. 1,901 mmHg·cm·s; P < 0.001) in the duodenum. In addition, the frequency of phase II propagated antroduodenal contractions was lower (5 vs. 11 per hour; P < 0.001) in patients compared with HV. Interestingly, the antral CI/s of phase III was decreased in FD patients but not in IBS patients. Patients with severe DGBI display alterations in antral and intestinal motility assessed by commercially available HR-ADM. Whether these alterations may explain symptom profiles in such patients remains to be confirmed (NCT04918329 and NCT01519180).NEW & NOTEWORTHY Gastrointestinal dysmotility has been assessed poorly in disorders of gut-brain interaction (DGBI), especially with high-resolution antroduodenal manometry. Plots of DGBI patients showed lower duodenal contractions during phase II regarding amplitude, frequency, and contractile integral/sensor (CI/s) compared with healthy volunteers. A lower frequency of propagated antroduodenal contractions was also reported. Finally, antral CI/s was lower in patients with functional dyspepsia during phase III. Further studies are needed to assess the clinical significance of these alterations.

RhoA downregulation in the murine intestinal epithelium results in chronic Wnt activation and increased tumorigenesis

Rho GTPases are molecular switches regulating multiple cellular processes. To investigate the role of RhoA in normal intestinal physiology, we used a conditional mouse model overexpressing a dominant negative RhoA mutant (RhoAT19N) in the intestinal epithelium. Although RhoA inhibition did not cause an overt phenotype, increased levels of nuclear β-catenin were observed in the small intestinal epithelium of RhoAT19N mice, and the overexpression of multiple Wnt target genes revealed a chronic activation of Wnt signaling. Elevated Wnt signaling in RhoAT19N mice and intestinal organoids did not affect the proliferation of intestinal epithelial cells but significantly interfered with their differentiation. Importantly, 17-month-old RhoAT19N mice showed a significant increase in the number of spontaneous intestinal tumors. Altogether, our results indicate that RhoA regulates the differentiation of intestinal epithelial cells and inhibits tumor initiation, likely through the control of Wnt signaling, a key regulator of proliferation and differentiation in the intestine.

Estrogens Play a Critical Role in Stress-Related Gastrointestinal Dysfunction in a Spontaneous Model of Disorders of Gut-Brain Interaction

BACKGROUND

Disorders of the gut-brain interaction (DGBI), such as irritable bowel syndrome and functional dyspepsia, are more prevalent in women than in men, with a ratio of 2:1. Furthermore, stressful life events have been reported as one of the triggers for symptoms in DGBI patients.

METHODS

Here, we studied the effect of an early-life stressor (maternal separation (MS)) on jejunal and colonic alterations, including colonic sensitivity and immune cells infiltration and activation in a validated spontaneous model of DGBI (BBDP-N), and investigated the involvement of β-estradiol on stress-worsened intestinal alterations.

RESULTS

We found that maternal separation exacerbated colonic sensitivity and mast cell and eosinophil infiltration and activation in females only. Ovariectomy partially rescued the stress phenotype by decreasing colonic sensitivity, which was restored by β-estradiol injections and did not impact immune cells infiltration and activation. Stressed males exposed to β-estradiol demonstrated similar intestinal alterations as MS females.

CONCLUSION

Estrogen plays a direct critical role in colonic hypersensitivity in a spontaneous animal model of DGBI, while for immune activation, estrogen seems to be involved in the first step of their recruitment and activation. Our data point towards a complex interaction between stress and β-estradiol in DGBI.

The Role of Leaky Gut in Functional Dyspepsia

Patients with functional dyspepsia (FD) complain of epigastric symptoms with no identifiable cause. Increased intestinal permeability has been described in these patients, especially in the proximal small bowel or duodenum, and was associated with mucosal immune activation and symptoms. In this review, we discuss duodenal barrier function, including techniques currently applied in FD research. We summarize the available data on duodenal permeability in FD and factors associated to increased permeability, including mucosal eosinophils, mast cells, luminal and systemic factors. While the increased influx of antigens into the duodenal mucosa could result in local immune activation, clinical evidence for a causal role of permeability is lacking in the absence of specific barrier-protective treatments. As both existing and novel treatments, including proton pump inhibitors (PPI) and pre- or probiotics may impact duodenal barrier function, it is important to recognize and study these alterations to improve the knowledge and management of FD.

Intestinal Mucosal Barrier Is Regulated by Intestinal Tract Neuro-Immune Interplay

Inflammatory bowel disease, irritable bowel syndrome and severe central nervous system injury can lead to intestinal mucosal barrier damage, which can cause endotoxin/enterobacteria translocation to induce infection and is closely related to the progression of metabolic diseases, cardiovascular and cerebrovascular diseases, tumors and other diseases. Hence, repairing the intestinal barrier represents a potential therapeutic target for many diseases. Enteral afferent nerves, efferent nerves and the intrinsic enteric nervous system (ENS) play key roles in regulating intestinal physiological homeostasis and coping with acute stress. Furthermore, innervation actively regulates immunity and induces inherent and adaptive immune responses through complex processes, such as secreting neurotransmitters or hormones and regulating their corresponding receptors. In addition, intestinal microorganisms and their metabolites play a regulatory role in the intestinal mucosal barrier. This paper primarily discusses the interactions between norepinephrine and β-adrenergic receptors, cholinergic anti-inflammatory pathways, nociceptive receptors, complex ENS networks, gut microbes and various immune cells with their secreted cytokines to summarize the key roles in regulating intestinal inflammation and improving mucosal barrier function.

Recent Advances in the Definition and Management of Functional Dyspepsia

In 2016, the Rome criteria were updated as Rome IV, and only minor changes were introduced for functional dyspepsia (FD). The major symptoms of FD now include not only postprandial fullness, but also epigastric pain and burning, and early satiation at above the "bothersome" level. Investigations into the effect of meal ingestion on symptom generation have indicated that not only postprandial fullness and early satiety but also epigastric pain and burning sensation and nausea (not vomiting) may increase after meals. Helicobacter pylori infection is considered to be the cause of dyspepsia if successful eradication leads to sustained resolution of symptoms for more than 6 months, and such a condition has been termed H. pylori-associated dyspepsia. Prompt esophagogastroduodenoscopy and H. pylori "test and treat" may be beneficial, especially in regions with a high prevalence of gastric cancer, such as east Asia. In terms of treatment, acotiamide, tandospirone, and rikkunshito are newly listed in Rome IV as treatment options for FD. Clinical studies in the field of FD should be strictly based on the Rome IV criteria until the next Rome V is published in 2026.

Functional dyspepsia

Dyspepsia is a complex of symptoms referable to the gastroduodenal region of the gastrointestinal tract and includes epigastric pain or burning, postprandial fullness, or early satiety. Approximately 80% of individuals with dyspepsia have no structural explanation for their symptoms and have functional dyspepsia. Functional dyspepsia affects up to 16% of otherwise healthy individuals in the general population. Risk factors include psychological comorbidity, acute gastroenteritis, female sex, smoking, use of non-steroidal anti-inflammatory drugs, and Helicobacter pylori infection. The pathophysiology remains incompletely understood, but it is probably related to disordered communication between the gut and the brain, leading to motility disturbances, visceral hypersensitivity, and alterations in gastrointestinal microbiota, mucosal and immune function, and CNS processing. Although technically a normal endoscopy is required to diagnose functional dyspepsia, the utility of endoscopy in all patients with typical symptoms is minimal; its use should be restricted to people aged 55 years and older, or to those with concerning features, such as weight loss or vomiting. As a result of our incomplete understanding of its pathophysiology, functional dyspepsia is difficult to treat and, in most patients, the condition is chronic and the natural history is one of fluctuating symptoms. Eradication therapy should be offered to patients with functional dyspepsia who test positive for Helicobacter pylori. Other therapies with evidence of effectiveness include proton pump inhibitors, histamine-2 receptor antagonists, prokinetics, and central neuromodulators. The role of psychological therapies is uncertain. As our understanding of the pathophysiology of functional dyspepsia increases, it is probable that the next decade will see the emergence of truly disease-modifying therapies for the first time.

Analysis of Postprandial Symptom Patterns in Subgroups of Patients With Rome III or Rome IV Functional Dyspepsia

BACKGROUND & AIMS

Among patients with functional dyspepsia (FD), there is overlap in symptoms between those in the Rome III subgroups of postprandial distress syndrome (PDS) and those with epigastric pain syndrome (EPS). The Rome IV consensus proposed to incorporate all patients with postprandial symptoms into the PDS group. We aimed to evaluate the assessment of meal-related dyspepsia symptoms in patients with FD according to the Rome III vs Rome IV subdivisions.

METHODS

Consecutive patients with FD referred for a gastric emptying test (n = 96) were asked to fill out the Rome III gastroduodenal questionnaire, with questions on meal-related occurrence. Study participants underwent a gastric emptying breath test, during which the intensity of dyspeptic symptoms (fullness, bloating, belching, nausea, epigastric pain, and burning) was scored before and up to 4 hours after a meal. We analyzed the association between the Rome subdivision and symptom severity and pattern during the breath test.

RESULTS

According to Rome III, 10% had EPS alone, 29% PDS alone, and 61% overlapping EPS and PDS. The frequency of the symptoms reported in the Rome questionnaire associated with the intensity of the symptoms during the breath test in the PDS group and in the groups with PDS and EPS overlap, but not in the group with EPS. We adapted the definition of the PDS subgroup to include patients with meal-related non-PDS symptoms (Rome IV); this reduced the proportion of patients with overlap of EPS and PDS symptoms from 61% to 18% and in this group the association of symptoms with the meal was reduced.

CONCLUSIONS

In an analysis of patients with FD, a meal induced or exacerbated symptoms in most patients. The Rome IV criteria for PDS reduce the proportions categorized as having both PDS and EPS and identify a patient group whose symptoms are associated with the meals. University hospital of Leuven study no: S55426.

Animal Models for Functional Gastrointestinal Disorders

Functional gastrointestinal disorders (FGID), such as functional dyspepsia (FD) and irritable bowel syndrome (IBS) are characterized by chronic abdominal symptoms in the absence of an organic, metabolic or systemic cause that readily explains these complaints. Their pathophysiology is still not fully elucidated and animal models have been of great value to improve the understanding of the complex biological mechanisms. Over the last decades, many animal models have been developed to further unravel FGID pathophysiology and test drug efficacy. In the first part of this review, we focus on stress-related models, starting with the different perinatal stress models, including the stress of the dam, followed by a discussion on neonatal stress such as the maternal separation model. We also describe the most commonly used stress models in adult animals which brought valuable insights on the brain-gut axis in stress-related disorders. In the second part, we focus more on models studying peripheral, i.e., gastrointestinal, mechanisms, either induced by an infection or another inflammatory trigger. In this section, we also introduce more recent models developed around food-related metabolic disorders or food hypersensitivity and allergy. Finally, we introduce models mimicking FGID as a secondary effect of medical interventions and spontaneous models sharing characteristics of GI and anxiety-related disorders. The latter are powerful models for brain-gut axis dysfunction and bring new insights about FGID and their comorbidities such as anxiety and depression.

Colonic hypersensitivity and low-grade inflammation in a spontaneous animal model for functional gastrointestinal disorders

BACKGROUND

A complex interplay between a failing intestinal barrier and low-grade inflammation leading to sensorimotor disturbances is an often-cited mechanism in the pathogenesis of functional gastrointestinal disorders (FGID). However, the cause-consequence relationship between these features has not been clearly established. We previously described jejunal alterations in the normoglycemic BB-rat (BBDP-N) model proposing this model as a suitable animal model to study FGID pathophysiology. The current study explores colonic permeability, inflammation, and sensitivity of the BB-rat.

METHODS

Colonic tissue of BBDP-N and control (BBDR) rats at 50, 90, 110, 160, and 220 days (n ≥ 7 per group) was used to assess intestinal permeability in Ussing chambers and inflammation, including infiltration by eosinophils, mast cells, and eosinophil peroxidase (EPO) activity. Anxiety-like symptoms were evaluated at 50, 90, and 220 days and colonic sensitivity at 160 and 220 days by measuring the visceromotor response (VMR) to isobaric colorectal distensions.

KEYS RESULTS

Lamina propria eosinophil and mast cell infiltration and increased EPO activity were demonstrated from 90 days onward. Increased permeability and myenteric ganglionitis were observed in the oldest BBDP-N rats. At 220 days, the VMR was significantly increased suggesting colonic hypersensitivity. At the same age, increased anxiety-like behavior was observed.

CONCLUSION AND INFERENCES

We demonstrated a lamina propria eosinophil and mast cell infiltration preceding visceral hypersensitivity in the colon of the BBDP-N rat, reminiscent of patients with FGID. These findings help elucidating pathogenetic pathways in FGID and further validate the BBDP-N rat as an attractive model to study pathophysiology and therapy of FGID.

Enteric Glial Dysfunction Evoked by Apolipoprotein E Deficiency Contributes to Delayed Gastric Emptying

BACKGROUND AND AIM

Diabetes is the main cause of gastroparesis accompanying decreased neuronal nitric oxide synthase (nNOS) in myenteric ganglia of the stomach. Decreased nNOS expression in the stomach also results from defects in apolipoprotein E (ApoE), which is secreted by astrocytes and has neuroprotective effects on the central nervous system. However, the roles of ApoE and enteric glial cells on gastric motility are uncertain. In this study, ApoE and enteric glial cell alterations in gastroparesis were investigated.

METHODS

Type 2 diabetic (db/db) mice and ApoE-knockout mice were analyzed. Gastric emptying was measured using the ¹³C acetic acid breath test. Expression levels of the pan-neuronal marker, protein gene product 9.5 (PGP 9.5), and glial marker, glial fibrillary acidic protein (GFAP) were examined by immunohistochemistry. Neural stem cells (NSCs) were injected into the gastric antral wall of ApoE-knockout mice.

RESULTS

Delayed gastric emptying was observed in 27% of db/db mice with significant decreases in serum ApoE levels and GFAP expression in the gastric antrum. Gastric emptying was also delayed in ApoE-knockout mice, with a significant decrease in GFAP expression, but no change in PGP 9.5 expression. Transplantation of NSCs improved gastric emptying in ApoE-knockout mice through supplementation of GFAP-positive cells.

CONCLUSIONS

Our results suggest that decreased enteric glial cells in ApoE-knockout mice are crucial for development of delayed gastric emptying, and NSC transplantation is effective in restoring myenteric ganglia and gastric motility.

Subacute stress and chronic stress interact to decrease intestinal barrier function in rats

Psychological stress increases intestinal permeability, potentially leading to low-grade inflammation and symptoms in functional gastrointestinal disorders. We assessed the effect of subacute, chronic and combined stress on intestinal barrier function and mast cell density. Male Wistar rats were allocated to four experimental groups (n = 8/group): 1/sham; 2/subacute stress (isolation and limited movement for 24 h); 3/chronic crowding stress for 14 days and 4/combined subacute and chronic stress. Jejunum and colon were collected to measure: transepithelial electrical resistance (TEER; a measure of epithelial barrier function); gene expression of tight junction molecules; mast cell density. Plasma corticosterone concentration was increased in all three stress conditions versus sham, with highest concentrations in the combined stress condition. TEER in the jejunum was decreased in all stress conditions, but was significantly lower in the combined stress condition than in the other groups. TEER in the jejunum correlated negatively with corticosterone concentration. Increased expression of claudin 1, 5 and 8, occludin and zonula occludens 1 mRNAs was detected after subacute stress in the jejunum. In contrast, colonic TEER was decreased only after combined stress, and the expression of tight junction molecules was unaltered. Increased mast cell density was observed in the chronic and combined stress condition in the colon only. In conclusion, our data show that chronic stress sensitizes the gastrointestinal tract to the effects of subacute stress on intestinal barrier function; different underlying cellular and molecular alterations are indicated in the small intestine versus the colon.

Abnormal Barrier Function in Gastrointestinal Disorders

There is increasing concern in identifying the mechanisms underlying the intimate control of the intestinal barrier, as deregulation of its function is strongly associated with digestive (organic and functional) and a number of non-digestive (schizophrenia, diabetes, sepsis, among others) disorders. The intestinal barrier is a complex and effective defensive functional system that operates to limit luminal antigen access to the internal milieu while maintaining nutrient and electrolyte absorption. Intestinal permeability to substances is mainly determined by the physicochemical properties of the barrier, with the epithelium, mucosal immunity, and neural activity playing a major role. In functional gastrointestinal disorders (FGIDs), the absence of structural or biochemical abnormalities that explain chronic symptoms is probably close to its end, as recent research is providing evidence of structural gut alterations, at least in certain subsets, mainly in functional dyspepsia (FD) and irritable bowel syndrome (IBS). These alterations are associated with increased permeability, which seems to reflect mucosal inflammation and neural activation. The participation of each anatomical and functional component of barrier function in homeostasis and intestinal dysfunction is described, with a special focus on FGIDs.

The role for gut permeability in the pathogenesis of type 1 diabetes--a solid or leaky concept?

Increasing evidence, both functional and morphological, supports the concept of increased intestinal permeability as an intrinsic characteristic of type 1 diabetes (T1D) in both humans and animal models of the disease. Often referred to as a 'leaky gut', its mechanistic impact on the pathogenesis of T1D remains unclear. Hypotheses that this defect influences immune responses against antigens (both self and non-self) predominate, yet others argue hyperglycemia and insulitis may contribute to increased gut permeability in T1D. To address these complicated issues, we herein review the many conceptual role(s) for a leaky gut in the pathogenesis of T1D and suggest ways that if true, therapeutic interventions aimed at the gut-pancreas axis may prove promising for future therapeutic interventions.