The role of serotonin in irritable bowel syndrome: implications for management

Somatization is associated with altered serum levels of vitamin D, serotonin, and brain-derived neurotrophic factor in patients with predominant diarrhea irritable bowel syndrome

BACKGROUND

Patients with irritable bowel syndrome (IBS) often show psychological disorders, including somatization, usually driven by an altered gut-brain axis. These changes are also accompanied by modifications in the circulating levels of vitamin D (VD) and neurotransmitters such as serotonin (5-HT) and brain-derived neurotrophic factor (BDNF). The present study aimed to evaluate the relationship between gastrointestinal (GI) symptoms and circulating levels of VD, 5-HT, and BDNF in IBS patients with diarrhea (IBS-D) categorized according to somatization.

METHODS

Fifty-three IBS-D patients were recruited and profiled for GI symptoms by validated questionnaires. The fasting serum concentrations of VD, 5-HT, and BDNF were assessed. The health of the intestinal barrier, minimal inflammation, and dysbiosis was also evaluated.

KEY RESULTS

Thirty patients showed high somatization scores, IBS-D(S+), and 23 low somatization scores, IBS-D(S-). IBS-D(S+) patients reported higher "Abdominal pain" and the "Abdominal pain duration in days" scores, lower serum VD levels and increased 5-HT and BDNF concentrations than IBS-D(S-). Besides, in IBS-D(S+) patients, the GI symptoms correlated with 5HT, BDNF, and VD concentrations. These parameters were associated with impaired small intestinal permeability and increased inflammation markers.

CONCLUSIONS AND INFERENCES

These data support the multifactorial IBS pathogenesis in which organic and psychological factors interact. An active role by VD, 5-HT, and BDNF in affecting the clinical and biochemical profiles in IBS-D(S+) patients may be conceivable. Therefore, the routine VD estimation and the assay of circulating levels of 5-HT and BDNF could be considered a new approach for managing these patients.

Modulation of Intestinal Corticotropin-Releasing Hormone Signaling by the Herbal Preparation STW 5-II: Possible Mechanisms for Irritable Bowel Syndrome Management

Corticotropin-releasing factor (CRF) mediates stress responses and alters the gut-brain axis, contributing to the pathogenesis of irritable bowel syndrome (IBS), which is recognized by abdominal pain accompanied by bowel habit disturbance. STW 5-II, a mixture of six herbal extracts, is clinically effective in functional dyspepsia and IBS. Here we aimed to establish an organoid-based stress-induced IBS-like model to investigate the mechanisms of action of STW 5-II. STW 5-II (10, 20, and 30 g/mL) was applied to intestinal organoids for 24 h before being treated with CRF (100 nM) for 48 h. The effects of STW 5-II on CRF signaling were investigated using several in vitro and in silico approaches. STW 5-II activities were further explored by in silico PyRx screening followed by molecular docking of the main 52 identified compounds in STW 5-II with both CRF receptors CRFR1 and CRFR2. CRF exposure stimulated inflammation and increased proinflammatory mediators, while STW 5-II dose-dependently counteracted these effects. STW 5-II inhibited CRF-induced claudin-2 overexpression and serotonin release. Docking of the STW 5-II constituents oleanolic acid and licorice saponin G2 to CRFR1 and CRFR2, respectively, showed a good affinity. These multi-target activities support and elucidate the clinically proven efficacy of STW 5-II in disorders of gut-brain interaction.

Effects of vitamin D3 supplementation on clinical symptoms, quality of life, serum serotonin (5-hydroxytryptamine), 5-hydroxy-indole acetic acid, and ratio of 5-HIAA/5-HT in patients with diarrhea-predominant irritable bowel syndrome: A randomized clinical trial

Vitamin D deficiency, common in the population with irritable bowel syndrome (IBS), can induce the main factors that lead to IBS clinical symptoms, such as depression, anxiety, and inflammation. Serotonin (5-HT) plays an important role in the pathophysiology of IBS, and its production and secretion are increased from the lumen due to stress and inflammation. The aim of this study was to evaluate the effect of vitamin D3 supplementation on the pathogenesis of diarrhea-predominant IBS (IBS-D). Seventy-four IBS-D patients (age: 18-65 y) participated in a randomized, double-blind, placebo-controlled trial study from February 2017 to May 2018, at Rasoul-e-Akram Hospital, Tehran, Iran. Subjects were allocated into two groups receiving 50,000 IU/week of vitamin D3 or placebo for 9 weeks. IBS severity score system (IBS-SSS), IBS-quality of life questionnaire (QoL), hospital anxiety and depression Scale (HADs), visceral sensitivity index (VSI) and serum 25(OH) vitamin D3, serotonin, 5-hydroxy-indole acetic acid and ratio of 5-HIAA/5-HT were evaluated before and after the interventions. Symptoms severity, QoL, HADs-depression, and VSI score improved significantly in the vitamin D group as compared to the placebo group (P-values: <0.001, 0.049, 0.023, and 0.008; respectively). There were no significant differences in abdominal bloating, HADs-anxiety, serum 5-HT, 5-HIAA, and 5-HIAA/5-HT between the two groups at the end of the study. Based on our results, we recommend serum vitamin D be evaluated in the process of treatment of these patients to ameliorate symptoms and quality life of IBS-D patients with vitamin D deficiency and/or insufficiency.

Functional polymorphism of the serotonin reuptake transporter SLC6A4 gene in various clinical variants of irritable bowel syndrome

Rationale:Irritable bowel syndrome (IBS) is a multifactorial disease, the genetic aspect of which is being actively studied.

Aim:To investigate functional polymorphism of the serotonin reuptake transporter (SERT)SLC6A4gene of various clinical variants of IBS.

Materials and methods:We performed a cross-sectional single center study in 79 Caucasian patients with IBS (according to the Rome criteria IV). The patients were divided into two groups: group 1, IBS with diarrhea (IBS-D, n = 45) and group 2, IBS with constipation (IBS-C, n = 34). The control group included 59 Caucasian patients with gastrointestinal disorders without IBS. Polymorphism5-HTTLPRof theSLC6A4gene was assessed in all subjects. In group 1 patients, blood serotonin levels were measured and psychological tests were performed, including Spielberger's State / Trait Anxiety Inventory, quality of life by SF36 and GSRS, Asthenia scale, VAS scores for pain intensity.

Results:Thirty-five of 45 (77.8%) patients with IBS-D carried the mutantSallele, which was significantly more frequent than in the IBS-C group (p = 0.002) and in the control group (p = 0.005). There were no statistically significant differences (p = 0.54) in the frequency of detection of the homozygousLLgenotype (normal allele) and the heteroand homozygous mutant alleles (SLandSS) genotype between the IBS-C and control patients. In the IBS-D group, a gender difference for the mutantSSallele of5-HTTLPRwas found, with significantly higher frequency in female patients (p = 0.0147). No significant gender differences in the genotype distribution between the patients with IBS-C and the control group were found. There were also no differences in blood serotonin levels in the IBS patients with various5-HTTLPRtypes (p = 0.086); they were all in the reference range. However, there was a trend towards lower serotonin levels in theLLgenotype carriers compared to those with theSS/SLpolymorphisms. The Gastroenterological inventoryGSRSdemonstrated significantly higher total score for the constipation syndrome in the patients with homozygousLL 5-HTTLPRpolymorphism, compared to that in the patients with theSS/SLgenotype (p = 0.013).

Conclusion:The results may be related to lower expression of theSLC6A4gene in the carriers of the mutant allele in the5-HTTLPRpromoter and subsequent decreased rate of serotonin uptake, with resulting stimulation of the gastrointestinal tract. TheSERTpolymorphism of theSLC6A4gene is worth further investigation as a potential candidate gene in the IBS pathophysiology.

The complex interplay between gastrointestinal and psychiatric symptoms in irritable bowel syndrome: A longitudinal assessment

AIMS

The aims of this study were to better define the relationship between irritable bowel syndrome (IBS) and psychiatric disorders and to examine the efficacy of paroxetine in the treatment of IBS patients.

METHODS

One hundred fifty subjects with diagnosis of IBS (Roma III criteria) and relative sub-classification (constipated, diarrhea, and mixed) were assessed for psychopathological features and gastrointestinal symptoms using IBS Symptom Severity Score and were consecutively enrolled. Fifty patients assumed paroxetine for 16 weeks and were longitudinally evaluated.

RESULTS

The entire sample had a moderate/severe gastrointestinal symptomatology (IBS-SSS 285.1 ± 98.6). The IBS subtypes were diarrhea (47.3%), constipated (32%), and mixed (20.7%). Panic disorder was found in 17.4% and major depressive episode in 14.7%. More than 50% of the patients showed "psychopathological features." This group showed more severe gastrointestinal symptoms and worse quality of life than the group without any psychiatric comorbidity (44%). Psychiatric patients also showed a significant impairment of physical state, subjective feeling of well-being, and leisure activities when compared with no psychiatric patients. When the IBS-SSS > 300 group was subgrouped in psychiatric (67.2%) and no psychiatric (32.8%), we found significant differences in all clinician-administered and self-reported scales with more severe psychopathological features in psychiatric group (P < 0.01). Among the patients treated with paroxetine, 34 (68%) completed the longitudinal evaluation showing a significant improvement of both psychiatric and gastrointestinal symptoms.

CONCLUSIONS

This study confirms a high presence of psychiatric comorbidities, emphasizing the need for psychiatric screening in all patients with IBS; moreover, the longitudinal evaluation of patients treated with paroxetine showed a significant improvement of both psychiatric and gastrointestinal symptoms.

What We Know and What We Need to Know about Aromatic and Cationic Biogenic Amines in the Gastrointestinal Tract

Biogenic amines derived from basic and aromatic amino acids (B/A-BAs), polyamines, histamine, serotonin, and catecholamines are a group of molecules playing essential roles in many relevant physiological processes, including cell proliferation, immune response, nutrition and reproduction. All these physiological effects involve a variety of tissue-specific cellular receptors and signalling pathways, which conforms to a very complex network that is not yet well-characterized. Strong evidence has proved the importance of this group of molecules in the gastrointestinal context, also playing roles in several pathologies. This work is based on the hypothesis that integration of biomedical information helps to reach new translational actions. Thus, the major aim of this work is to combine scientific knowledge on biomolecules, metabolism and physiology of the main B/A-BAs involved in the pathophysiology of the gastrointestinal tract, in order to point out important gaps in information and other facts deserving further research efforts in order to connect molecular information with pathophysiological observations.

The relationship between lower urinary tract symptoms and irritable bowel syndrome: a meta-analysis of cross-sectional studies

INTRODUCTION

While several epidemiologic studies have investigated the relationship between lower urinary tract symptoms (LUTS) and irritable bowel syndrome (IBS), it remains unclear. To investigate the relationship between IBS and LUTS, a systematic review and meta-analysis of cross-sectional studies was carried out.

EVIDENCE ACQUISITION

Online databases were searched up to December 1st, 2017 for cross-sectional studies that evaluated the association between IBS and the risk of LUTS. Summary odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated.

EVIDENCE SYNTHESIS

In all, 9 articles that contained 19907 participants and 2620 cases of LUTS were included in this meta-analysis. Compared with the non-IBS group, the IBS group had a higher risk of LUTS (total OR=2.11, 95% CI: 1.91-2.33, P<0.00001). Patients with IBS were more likely to have urine storage symptoms (total OR=1.80, 95% CI: 1.34-2.42, P<0.0001). Subgroup analysis by gender showed that the IBS group had a higher risk of LUTS in both men (total OR=2.17, 95% CI: 1.82-2.58, P<0.00001) and women (total OR=1.85, 95% CI: 1.57-2.17, P<0.00001).

CONCLUSIONS

Our meta-analysis provides evidence that IBS is associated with an increased risk of LUTS in both men and women.

Serotonin 5-HT2A receptor activation blocks TNF-α mediated inflammation in vivo

Tumor necrosis factor alpha (TNF-α) plays a key role in inflammation, and its production and signaling contribute to many inflammatory related diseases. Recently, we discovered that selective activation of serotonin 5-HT2A receptors with the agonist (R)-DOI produces a super-potent blockade of proinflammatory markers in primary rat aortic smooth muscle cells. Here, we demonstrate that systemic administration of (R)-DOI can block the systemic effects of TNF-α in whole animal, with potent anti-inflammatory effects in the aortic arch and small intestine. This includes blockade of TNF-α-induced expression of pro-inflammatory cell adhesion (Icam-1, Vcam-1), cytokine (Il-6, IL-1b), and chemokine (Mcp-1, Cx3cl1) genes, and expression of VCAM-1 protein in the intestine. Further, systemic (R)-DOI also prevents the TNF-α-induced increase of circulating IL-6. Importantly, utilizing receptor selective antagonists, we have demonstrated that the mechanism underlying the systemic anti-inflammatory effects of (R)-DOI is activation of serotonin 5-HT2A receptors. Our results highlight a powerful new role for the serotonin 5-HT2A receptor in inflammatory processes, and indicate that agonism of serotonin receptors may represent an effective and novel approach to develop powerful small molecule therapeutics for inflammatory diseases and conditions such as atherosclerosis and inflammatory bowel disease.

Relationship between overactive bladder and irritable bowel syndrome: a large-scale internet survey in Japan using the overactive bladder symptom score and Rome III criteria

WHAT'S KNOWN ON THE SUBJECT? AND WHAT DOES THE STUDY ADD?: There is known to be an association between overactive bladder (OAB) and irritable bowel syndrome (IBS). The study investigates the association between OAB and IBS using an internet-based survey in Japan. It is the first to investigate the prevalence and severity of OAB in the general population using the OAB symptom score questionnaire.

OBJECTIVE

To investigate the association between overactive bladder (OAB) and irritable bowel syndrome (IBS) by using an internet-based survey in Japan.

SUBJECTS AND METHODS

Questionnaires were sent via the internet to Japanese adults. The overactive bladder symptom score was used for screening OAB, and the Japanese version of the Rome III criteria for the diagnosis of IBS was used for screening this syndrome.

RESULTS

The overall prevalence of OAB and IBS was 9.3% and 21.2%, respectively. Among the subjects with OAB, 33.3% had concurrent IBS. The prevalence of OAB among men was 9.7% and among women it was 8.9%, while 18.6% of men and 23.9% of women had IBS. Concurrent IBS was noted in 32.0% of men and 34.8% of women with OAB.

CONCLUSION

Taking into account a high rate of concurrent IBS in patients with OAB, it seems to be important for physicians to assess the defaecation habits of patients when diagnosing and treating OAB.

Brain-Gut Interactions in IBS

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder with an estimated prevalence of 10–20%. Current understanding of the pathophysiology of IBS is incomplete due to the lack of a clearly identified pathological abnormality and due to the lack of reliable biomarkers. Possible mechanisms believed to contribute to IBS development and IBS like symptoms include physical stressors, such as infection or inflammation, psychological, and environmental factors, like anxiety, depression, and significant negative life events. Some of these mechanisms may involve the brain-gut axis (BGA). In this article we review the current knowledge on the possible involvement of the BGA in IBS and discuss new directions for potential future therapies of IBS.

Serotonin transporter gene promoter region polymorphisms and serotonin transporter expression in the colonic mucosa of irritable bowel syndrome patients

BACKGROUND

The role of serotonin transporter (SERT) gene polymorphism in irritable bowel syndrome (IBS) has been demonstrated. However, the expression of SERT mRNA and proteins in the colonic mucosa with different 5-HTT gene-linked polymorphic region (5-HTTLPR) genotypes remains unknown. We examined SERT mRNA and protein levels in colon biopsies from patients with different 5-HTTLPR genotypes and evaluated the links between the polymorphism and the expression levels.

METHODS

Two hundred and fifty-four patients with IBS and 120 healthy subjects were studied. DNA samples were extracted from peripheral blood and genotyped by polymerase chain reaction (PCR). SERT mRNA and protein levels were evaluated by quantitative real time PCR and western blotting. The promoter efficiency of the serotonin transporter promoter (SERT-P) was evaluated with luciferase reporter system.

KEY RESULTS

The frequency of the L/L genotype in C-IBS group was significantly higher than that in the control and D-IBS. However, the S/S genotype in D-IBS was significantly higher than that in C-IBS. The transcriptional efficiency of the L/L genotype was significantly higher than that in the L/S and S/S genotype. Patients with the L/L genotype demonstrated increased production of the SERT protein when compared with L/S and S/S patients. The l variant increased SERT promoter activity by 2.43-fold when compared with the s variant.

CONCLUSIONS & INFERENCES

Polymorphism in the promoter region of the SERT gene can influence the expression of SERT mRNA and the levels of the SERT protein in the colonic mucosa, thereby playing a key role in motility-related symptoms of IBS patients.

Cytokine-induced alterations of gastrointestinal motility in gastrointestinal disorders

Inflammation and immune activation in the gut are usually accompanied by alteration of gastrointestinal (GI) motility. In infection, changes in motor function have been linked to host defense by enhancing the expulsion of the infectious agents. In this review, we describe the evidence for inflammation and immune activation in GI infection, inflammatory bowel disease, ileus, achalasia, eosinophilic esophagitis, microscopic colitis, celiac disease, pseudo-obstruction and functional GI disorders. We also describe the possible mechanisms by which inflammation and immune activation in the gut affect GI motility. GI motility disorder is a broad spectrum disturbance of GI physiology. Although several systems including central nerves, enteric nerves, interstitial cells of Cajal and smooth muscles contribute to a coordinated regulation of GI motility, smooth muscle probably plays the most important role. Thus, we focus on the relationship between activation of cytokines induced by adaptive immune response and alteration of GI smooth muscle contractility. Accumulated evidence has shown that Th1 and Th2 cytokines cause hypocontractility and hypercontractility of inflamed intestinal smooth muscle. Th1 cytokines downregulate CPI-17 and L-type Ca²⁺ channels and upregulate regulators of G protein signaling 4, which contributes to hypocontractility of inflamed intestinal smooth muscle. Conversely, Th2 cytokines cause hypercontractilty via signal transducer and activator of transcription 6 or mitogen-activated protein kinase signaling pathways. Th1 and Th2 cytokines have opposing effects on intestinal smooth muscle contraction via 5-hydroxytryptamine signaling. Understanding the immunological basis of altered GI motor function could lead to new therapeutic strategies for GI functional and inflammatory disorders.

Pharmacologic and complementary and alternative medicine therapies for irritable bowel syndrome

Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder characterized by episodic abdominal pain or discomfort in association with altered bowel habits (diarrhea and/or constipation). Other gastrointestinal symptoms, such as bloating and flatulence, are also common. A variety of factors are believed to play a role in the development of IBS symptoms, including altered bowel motility, visceral hypersensitivity, psychosocial stressors, altered brain-gut interactions, immune activation/low grade inflammation, alterations in the gut microbiome, and genetic factors. In the absence of biomarkers that can distinguish between IBS subgroups on the basis of pathophysiology, treatment of this condition is predicated upon a patient's most bothersome symptoms. In clinical trials, effective therapies have only offered a therapeutic gain over placebos of 7-15%. Evidence based therapies for the global symptoms of constipation predominant IBS (IBS-C) include lubiprostone and tegaserod; evidence based therapies for the global symptoms of diarrhea predominant IBS (IBS-D) include the probiotic Bifidobacter infantis, the nonabsorbable antibiotic rifaximin, and alosetron. Additionally, there is persuasive evidence to suggest that selected antispasmodics and antidepressants are of benefit for the treatment of abdominal pain in IBS patients. Finally, several emerging therapies with novel mechanisms of action are in development. Complementary and alternative medicine therapies including probiotics, herbal therapies and acupuncture are gaining popularity among IBS sufferers, although concerns regarding manufacturing standards and the paucity of high quality efficacy and safety data remain.

Low-grade inflammation plays a pivotal role in gastrointestinal dysfunction in irritable bowel syndrome

The pathogenesis of irritable bowel syndrome (IBS) is considered to be multifactorial and includes psychosocial factors, visceral hypersensitivity, infection, microbiota and immune activation. It is becoming increasingly clear that low-grade inflammation is present in IBS patients and a number of biomarkers have emerged. This review describes the evidence for low-grade inflammation in IBS and explores its mechanism with particular focus on gastrointestinal motor dysfunction. Understanding of the immunological basis of the altered gastrointestinal motor function in IBS may lead to new therapeutic strategies for IBS.

Brain serotonergic circuitries

Brain serotonergic circuitries interact with other neurotransmitter systems on a multitude of different molecular levels. In humans, as in other mammalian species, serotonin (5-HT) plays a modulatory role in almost every physiological function. Furthermore, serotonergic dysfunction is thought to be implicated in several psychiatric and neurodegenerative disorders. We describe the neuroanatomy and neurochemistry of brain serotonergic circuitries. The contribution of emergent in vivo imaging methods to the regional localization of binding site receptors and certain aspects of their functional connectivity in correlation to behavior is also discussed. 5-HT cell bodies, mainly localized in the raphe nuclei, send axons to almost every brain region. It is argued that the specificity of the local chemocommunication between 5-HT and other neuronal elements mainly depends on mechanisms regulating the extracellular concentration of 5-HT the diversity of high-affinity membrane receptors, and their specific transduction modalities.

Pathogenic factors involved in the development of irritable bowel syndrome: focus on a microbial role

Irritable bowel syndrome (IBS) is a symptom complex characterized by recurrent abdominal pain or discomfort, and accompanied by abnormal bowel habits, in the absence of any discernible organic abnormality. Its origin remains unclear, partly because multiple pathophysiologic mechanisms are likely to be involved. A significant proportion of patients develop IBS symptoms after an episode of gastrointestinal infection. In addition to gastrointestinal pathogens, recent evidence suggests that patients with IBS have abnormal composition and higher temporal instability of their intestinal microbiota. Because the intestinal microbiota is an important determinant of normal gut function and immunity, this instability may constitute an additional mechanism that leads to symptom generation and IBS. More importantly, a role for altered microbiota composition in IBS raises the possibility of therapeutic interventions through selective antibiotic or probiotic administration. The new concept of functional bowel diseases incorporates the bidirectional communication between the gut and the central nervous system (gut-brain axis), which may explain the multiple facets of IBS by linking emotional and cognitive centers of the brain with peripheral functioning of the gastrointestinal tract and vice versa.

Effects of antidepressants in patients with irritable bowel syndrome and comorbid depression

BACKGROUND

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that affects up to 15% of community dwelling individuals. Psychiatric comorbidities, particularly symptoms of major depressive disorder (MDD), occur in up to 90% of patients with IBS.

OBJECTIVE

This article reviews the available literature on the use of antidepressants for both IBS and psychiatric depressive symptoms in patients with IBS.

METHODS

MEDLINE and International Pharmaceutical Abstracts (both, 1980-May 2010) were searched for English-language publications that involved antidepressant treatment of MDD in patients with IBS. The search terms were depression, irritable, bowel, treatment, and functional. The reference lists of key articles were searched for additional pertinent articles. Randomized controlled trials published in the past 10 years were given priority.

RESULTS

Of 46 articles identified by the literature search, 11 were included in the review: 4 studies of selective serotonin reuptake inhibitors (SSRIs), 4 of tricyclic antidepressants (TCAs), 1 comparing an SSRI and a TCA, 1 of the serotonin-norepinephrine reuptake inhibitor duloxetine, and a case report involving the tetracyclic antidepressant mirtazapine. Most of the identified studies excluded patients with a diagnosis of depression and/or anxiety. No controlled studies were identified in which the primary outcome was objective assessment of MDD symptoms in patients with IBS. Two of the SSRI studies, one of citalopram and the other of paroxetine, reported approximately 50% improvement in IBS symptoms (both studies, P = 0.01); the study of paroxetine reported a 30% improvement in scores on the Beck Depression Inventory (P = 0.01). The 2 studies of fluoxetine found no statistically significant benefit on IBS symptoms. TCAs were reported to have benefits on IBS symptoms, predominantly diarrhea. Only one of the TCA studies examined and found a significant improvement in depressive symptoms with desipramine 150 mg/d (P = 0.025). Both the open-label study of duloxetine and the case report involving mirtazapine found improvements in IBS and psychiatric symptoms.

CONCLUSIONS

The evidence for the benefit of antidepressant treatment in patients with IBS and comorbid depression was limited and contradictory. Some anti-depressants may help symptoms of IBS, although whether the same drugs and doses are associated with improvements in concomitant depressive symptoms remains to be elucidated.

Low-grade inflammation plays a pivotal role in gastrointestinal dysfunction in irritable bowel syndrome

The pathogenesis of irritable bowel syndrome (IBS) is considered to be multifactorial and includes psychosocial factors, visceral hypersensitivity, infection, microbiota and immune activation. It is becoming increasingly clear that low-grade inflammation is present in IBS patients and a number of biomarkers have emerged. This review describes the evidence for low-grade inflammation in IBS and explores its mechanism with particular focus on gastrointestinal motor dysfunction. Understanding of the immunological basis of the altered gastrointestinal motor function in IBS may lead to new therapeutic strategies for IBS.