The serotonin reuptake transporter is reduced in the epithelium of active Crohn's disease and ulcerative colitis

The 3 Ds: Depression, Dysbiosis, and Clostridiodes difficile

This paper explores the intricate relationship between depression, gut dysbiosis, and Clostridioides difficile infections, collectively termed "The 3 Ds". Depression is a widespread mental disorder increasing in prevalence. It is recognized for its societal burden and complex pathophysiology, encompassing genetic, environmental, and microbiome-related factors. The consequent increased use of antidepressants has led to growing concerns about their effects on the gut microbiome. Various classes of antidepressants and antipsychotics show antimicrobial activity, potentially leading to shifts in the gut microbiome and contributing to the development of dysbiosis. Dysbiosis, in turn, can predispose individuals to opportunistic infections like C. difficile, a significant healthcare concern due to its high recurrence rates and severe impact on patients' quality of life. Further, the link between antidepressant use and an increased risk of C. difficile infection (CDI) is explored and, finally, the emergence of live biotherapeutic products as novel treatment options for recurrent CDI is discussed.

Linking serotonin homeostasis to gut function: Nutrition, gut microbiota and beyond

Serotonin (5-HT) produced by enterochromaffin (EC) cells in the digestive tract is crucial for maintaining gut function and homeostasis. Nutritional and non-nutritional stimuli in the gut lumen can modulate the ability of EC cells to produce 5-HT in a temporal- and spatial-specific manner that toning gut physiology and immune response. Of particular interest, the interactions between dietary factors and the gut microbiota exert distinct impacts on gut 5-HT homeostasis and signaling in metabolism and the gut immune response. However, the underlying mechanisms need to be unraveled. This review aims to summarize and discuss the importance of gut 5-HT homeostasis and its regulation in maintaining gut metabolism and immune function in health and disease with special emphasis on different types of nutrients, dietary supplements, processing, and gut microbiota. Cutting-edge discoveries in this area will provide the basis for the development of new nutritional and pharmaceutical strategies for the prevention and treatment of serotonin homeostasis-related gut and systematic disorders and diseases.

Spatial features of skip lesions in Crohn's disease

Skip lesions are an enigmatic spatial feature characterizing Crohn's disease (CD). They comprise inflamed and adjacent non-inflamed tissue sections with a clear demarcation. Currently, spatial features of the human gastrointestinal (GI) system lack clarity regarding the organization of microbes, mucus, tissue, and host cells during inflammation. New technologies with multiplexing abilities and innovative approaches provide ways of examining the spatial organization of inflamed and non-inflamed tissues in CD, which may open new avenues for diagnosis, prognosis, and treatment. In this review, we present evidence of the relevance of spatial context in patients with CD and the methods and ideas recently published in studies of spatiality during inflammation. With this review, we aim to provide inspiration for further research to address existing gaps.

Modulation of Serotonin-Related Genes by Extracellular Vesicles of the Probiotic Escherichia coli Nissle 1917 in the Interleukin-1β-Induced Inflammation Model of Intestinal Epithelial Cells

Inflammatory bowel disease (IBD) is a chronic inflammatory condition involving dysregulated immune responses and imbalances in the gut microbiota in genetically susceptible individuals. Current therapies for IBD often have significant side-effects and limited success, prompting the search for novel therapeutic strategies. Microbiome-based approaches aim to restore the gut microbiota balance towards anti-inflammatory and mucosa-healing profiles. Extracellular vesicles (EVs) from beneficial gut microbes are emerging as potential postbiotics. Serotonin plays a crucial role in intestinal homeostasis, and its dysregulation is associated with IBD severity. Our study investigated the impact of EVs from the probiotic Nissle 1917 (EcN) and commensal E. coli on intestinal serotonin metabolism under inflammatory conditions using an IL-1β-induced inflammation model in Caco-2 cells. We found strain-specific effects. Specifically, EcN EVs reduced free serotonin levels by upregulating SERT expression through the downregulation of miR-24, miR-200a, TLR4, and NOD1. Additionally, EcN EVs mitigated IL-1β-induced changes in tight junction proteins and oxidative stress markers. These findings underscore the potential of postbiotic interventions as a therapeutic approach for IBD and related pathologies, with EcN EVs exhibiting promise in modulating serotonin metabolism and preserving intestinal barrier integrity. This study is the first to demonstrate the regulation of miR-24 and miR-200a by probiotic-derived EVs.

Serotonin Transporter Deficiency Induces Metabolic Alterations in the Ileal Mucosa

Serotonin transporter (SERT) deficiency has been implicated in metabolic syndrome, intestinal inflammation, and microbial dysbiosis. Interestingly, changes in microbiome metabolic capacity and several alterations in host gene expression, including lipid metabolism, were previously observed in SERT-/- mice ileal mucosa. However, the precise host or microbial metabolites altered by SERT deficiency that may contribute to the pleiotropic phenotype of SERT KO mice are not yet understood. This study investigated the hypothesis that SERT deficiency impacts lipid and microbial metabolite abundances in the ileal mucosa, where SERT is highly expressed. Ileal mucosal metabolomics was performed by Metabolon on wild-type (WT) and homozygous SERT knockout (KO) mice. Fluorescent-activated cell sorting (FACS) was utilized to measure immune cell populations in ileal lamina propria to assess immunomodulatory effects caused by SERT deficiency. SERT KO mice exhibited a unique ileal mucosal metabolomic signature, with the most differentially altered metabolites being lipids. Such changes included increased diacylglycerols and decreased monoacylglycerols in the ileal mucosa of SERT KO mice compared to WT mice. Further, the ileal mucosa of SERT KO mice exhibited several changes in microbial-related metabolites known to play roles in intestinal inflammation and insulin resistance. SERT KO mice also had a significant reduction in the abundance of ileal group 3 innate lymphoid cells (ILC3). In conclusion, SERT deficiency induces complex alterations in the ileal mucosal environment, indicating potential links between serotonergic signaling, gut microbiota, mucosal immunity, intestinal inflammation, and metabolic syndrome.

Serotonin deficiency from constitutive SKN-1 activation drives pathogen apathy

When an organism encounters a pathogen, the host innate immune system activates to defend against pathogen colonization and toxic xenobiotics produced. C. elegans employ multiple defense systems to ensure survival when exposed to Pseudomonas aeruginosa including activation of the cytoprotective transcription factor SKN-1/NRF2. Although wildtype C. elegans quickly learn to avoid pathogens, here we describe a peculiar apathy-like behavior towards PA14 in animals with constitutive activation of SKN-1, whereby animals choose not to leave and continue to feed on the pathogen even when a non-pathogenic and healthspan-promoting food option is available. Although lacking the urgency to escape the infectious environment, animals with constitutive SKN-1 activity are not oblivious to the presence of the pathogen and display the typical pathogen-induced intestinal distension and eventual demise. SKN-1 activation, specifically in neurons and intestinal tissues, orchestrates a unique transcriptional program which leads to defects in serotonin signaling that is required from both neurons and non-neuronal tissues. Serotonin depletion from SKN-1 activation limits pathogen defense capacity, drives the pathogen-associated apathy behaviors and induces a synthetic sensitivity to selective serotonin reuptake inhibitors. Taken together, our work reveals new insights into how animals perceive environmental pathogens and subsequently alter behavior and cellular programs to promote survival.

KEY POINTS

Identify an apathy-like behavioral response for pathogens resulting from the constitutive activation of the cytoprotective transcription factor SKN-1.Uncover the obligate role for serotonin synthesis in both neuronal and non-neuronal cells for the apathy-like state and ability of serotonin treatment to restore normal behaviors.Characterize the timing and tissue specificity of SKN-1 nuclear localization in neurons and intestinal cells in response to pathogen exposure.Define the unique and context-specific transcriptional signatures of animals with constitutive SKN-1 activation when exposed to pathogenic environments.Reveal necessity for both neuronal and non-neuronal serotonin signaling in host survival from pathogen infection.

Beyond the Brain: Perinatal Exposure of Rats to Serotonin Enhancers Induces Long-Term Changes in the Jejunum and Liver

Serotonin (5-hydroxytryptamine, 5HT) homeostasis is essential for many physiological processes in the central nervous system and peripheral tissues. Hyperserotonemia, a measurable sign of 5HT homeostasis disruption, can be caused by 5HT-directed treatment of psychiatric and gastrointestinal diseases. Its impact on the long-term balance and function of 5HT in the peripheral compartment remains unresolved and requires further research due to possible effects on human health. We explored the effects of perinatal 5HT imbalance on the peripheral organs responsible for serotonin metabolism-the jejunum, a synthesis site, and the liver, a catabolism site-in adult rats. Hyperserotonemia was induced by subchronic treatment with serotonin precursor 5-hydroxytryptophan (5HTP) or serotonin degradation inhibitor tranylcypromine (TCP). The jejunum and liver were collected on postnatal day 70 and analyzed histomorphometrically. Relative mRNA levels of 5HT-regulating proteins were determined using qRT-PCR. Compared to controls, 5HTP- and TCP-treated rats had a reduced number of 5HT-producing cells and expression of the 5HT-synthesising enzyme in the jejunum, and an increased expression of 5HT-transporter accompanied by karyomegaly in hepatocytes, with these differences being more pronounced in the TCP-treated animals. Here, we report that perinatal 5HT disbalance induced long-term cellular and molecular changes in organs regulating 5HT-metabolism, which may have a negative impact on 5HT availability and function in the periphery. Our rat model demonstrates a link between the developmental abnormalities of serotonin homeostasis and 5HT-related changes in adult life and may be suitable for exploring the neurobiological substrates of vulnerability to behavioral and metabolic disorders, as well as for modeling the adverse effects of the prenatal exposure to 5HT enhancers in the human population.

Collagenous Colitis with Escitalopram Use: A Case Report and Literature Review

We present the case of a 42-year-old female whose escitalopram use potentially contributed to a diagnosis of collagenous colitis. The patient presented with significant watery, nonbloody diarrhea, abdominal cramping and pain, and weight loss. Established risk factors of microscopic colitis in this patient include a history of smoking and female gender. The patient underwent a colonoscopy, which confirmed histological changes consistent with collagenous colitis. Prescribed therapy included oral budesonide and omeprazole, continued for eight and twelve weeks, respectively. Escitalopram was continued, with a discussion regarding changing to an alternative therapy. Based on the patient's history of escitalopram use, this case suggests a relationship between escitalopram and microscopic colitis. Though case reports of patients diagnosed with microscopic colitis after antidepressant use are published, this case appears to be the only report of collagenous colitis without macroscopic complications following escitalopram use. This case adds further support in that antidepressants may contribute to microscopic colitis. Despite an undefined frequency of association, healthcare providers who prescribe antidepressants should be cognizant of the theorized association and understand risk factors, screening, and treatment approaches.

Effects of in utero exposure to fluoxetine on the gastrointestinal tract of rat offspring

Perinatal exposure to selective serotonin reuptake inhibitors (SSRIs) has been shown to disrupt the development of serotonergic signaling pathways in the brain and enteric nervous system. Serotonin (5-hydroxytryptamine; 5-HT) signaling is critical for gastrointestinal homeostasis; changes in 5-HT expression and regulation have been associated with gastrointestinal diseases of motility and inflammation. We tested the hypothesis that perinatal exposure to the SSRI fluoxetine can influence the development of the gastrointestinal tract in exposed offspring. Female nulliparous Wistar rats were given fluoxetine (10 mg/kg) or vehicle control from 2 wk before mating until weaning; small and large intestines of female and male offspring were collected at postnatal days 1, 21 (P1, P21, respectively), and 6 mo of age. In histological preparations, the proportion of serotonergic neurons significantly increased in the colons of both female and male fluoxetine-exposed compared with control offspring at P21, a time point that signifies maximal exposure to fluoxetine. At 6 mo of age, male but not female fluoxetine-exposed offspring had a significant increase in circulating 5-HT, with a significant decrease in transcripts encoding the 5-HT2A receptor and monoamine oxidase as compared with control offspring. Measurement of spatiotemporal mapping of contractile activity of the small and large intestine at 6 mo of age revealed no changes in motility in the small bowel of fluoxetine-exposed offspring but revealed a significant increase in the frequency of colonic contractions in the female fluoxetine-exposed compared with control animals. Susceptibility to inflammation was examined at 6 mo using the dextran sulfate sodium model of acute colitis. In utero exposure to fluoxetine was not found to exacerbate colitis severity. These findings suggest that fluoxetine exposure during fetal and early postnatal development can lead to changes in serotonergic neurons at the peak of exposure with sex-specific changes in 5-HT signaling and colonic motility in adulthood.NEW & NOTEWORTHY There is increasing recognition of the relevance of in utero and early postnatal exposures in the developmental programming of the gastrointestinal tract. Perinatal exposure to selective serotonin reuptake inhibitors and antidepressant medications is of particular relevance as they are commonly prescribed during pregnancy, and serotonergic pathways play key roles during gastrointestinal development and in postnatal homeostasis. Here, we provide a comprehensive evaluation of clinically relevant outcomes of gastrointestinal motility and susceptibility to colitis in fluoxetine-exposed offspring and highlight changes in colonic serotonergic neurons at the peak of perinatal fluoxetine exposure with sex-dependent changes in serotonin signaling and colonic motility in adulthood.

Association between neuropeptides and mucins in Crohn's disease mucous cells

Crohn's disease (CD) and ulcerative colitis (UC) are both inflammatory bowel diseases (IBD). Unlike UC, which is limited to the mucosa of the colon, CD inflammation is characterized by chronic mucosal ulcerations affecting the entire gastrointestinal tract. Goblet cells (GCs) can be found in some lining epithelia, particularly in the respiratory and digestive tracts. GCs represent the main source of mucin that are the significant components of the mucus layer; hypertrophy of GCs and an increase in mucin production are observed in many enteric infections. The cytoplasm of goblet cells may also contain neuropeptides, such as serotonin, that can be altered in inflammatory bowel disease (IBD). The defense system of the gut is represented by the intestinal mucosal barrier, its protective function is strictly connected to the regulation of the mucus layer and the coordination of the neuro-immune response. Paraformaldehyde-fixed intestinal tissues, obtained from fifteen patients with Crohn's disease, were analyzed by immunostaining for MUC2, MUC4, 5-HT, and VAChT. This study aims to define the link between neuropeptides and mucins in mucous cells and their involvement in the inflammation process. Our results showed in mucous cells of Crohn's disease (CD) patients a high expression of MUC4 and a decrease in the expression of vesicular acetylcholine transporter (VAChT) demonstrating the presence of an inflammatory state.

The Effect of Serotonin Transmission on Depressive and Insomnia Symptoms in Inflammatory Bowel Diseases

The serotonergic pathway may impact the pathogenesis and the course of inflammatory bowel diseases (IBDs). The aim of this study was to investigate the relationship between 5-HT, the serotonin transporter (SERT), and the clinical course of the disease with the occurrence of sleep and mood disorders. Participants completed sleep questionnaires and the Beck Depression Inventory (BDI). Serum 5-HT, SERT protein expression, and mRNA levels were quantified. Additionally, patients treated with anti-TNF therapy were examined before and after treatment. In this study, 77 patients with IBD and 41 healthy controls (HCs) were enrolled and 24 of them were treated with anti-TNF therapy. Patients with IBD had higher 5-HT levels and SERT protein expression than the HCs, but not mRNA SERT levels (p = 0.015, p = 0.001, p = 0.069, respectively). Similar results were obtained for patients in the active state of the disease compared to the non-active state. There was a positive relationship between insomnia severity and SERT protein expression. BDI did not correlate with serotonin or SERT. After anti-TNF therapy, only 5-HT levels were decreased. 5-HT and SERT protein are overexpressed in active IBD and may represent a candidate for novel disease activity biomarkers. The correlation between the SERT protein level and the severity of insomnia symptoms might be among the underlying biochemical factors of sleep disturbances. Anti-TNF treatment might contribute to the reduction in 5-HT levels.

Limosilactobacillus mucosae and Lactobacillus amylovorus Protect Against Experimental Colitis via Upregulation of Colonic 5-Hydroxytryptamine Receptor 4 and Transforming Growth Factor-β2

BACKGROUND

Limosilactobacillusmucosae (LM) exerts anti-inflammatory and health-promoting effects. However, its role in the modulation of gut serotonin or 5-hydroxytryptamine (5-HT) metabolism and 5-HT receptors (HTRs) in inflammation requires further investigation.

OBJECTIVES

We compared LM with Lactobacillus amylovorus (LA) for the regulation of 5-HT, HTRs, inflammatory mediators, and their correlations in the colon of mice with experimental colitis.

METHODS

Male C57BL/6 mice were randomly assigned to 6 groups: control (Con), LM, LA, dextran sodium sulfate (DSS), and DSS with pre-administration of LM (+LM) or LA (+LA). After 7 d of DSS treatment, mice were killed to analyze the expression of inflammatory mediators, HTRs, and concentrations of 5-HT and microbial metabolites in the colon.

RESULTS

LM was more effective than LA in alleviating DSS-induced colonic inflammation. Compared with mice in the DSS group, mice receiving DSS + LM or DSS + LA treatment had lower (P < 0.05) colonic mRNA expression of proinflammatory cytokines. DSS + LM treatment had lower mRNA expression of Il1b, Tnfa, and Ccl3, an abundance of p-STAT3, and greater expression of Tgfb2 and Htr4 in the colon (P < 0.05). The expression of inflammatory mediators (including Tgfb-1) was positively correlated (P < 0.05) with 5-HT and Htr2a and negatively correlated (P < 0.05) with Htr4. However, the expression of Tgfb-2 showed reversed correlations with the 5-HT and HTRs described above. Patterns for these correlations were different for LM and LA. Mice receiving the DSS + LM treatment had greater (P < 0.05) concentrations of acetate and valerate and lower (P < 0.05) concentrations of indole-3-acetic acid in the cecal and colonic contents.

CONCLUSIONS

LM showed greater efficacy than LA in alleviating DSS-induced colonic inflammation. The coordinated regulation of transforming growth factor-β subtypes and serotonin receptors in the colon may be one of the most important mechanisms underlying the probiotic effects of lactobacilli in gut inflammation.

Lipids regulate peripheral serotonin release via gut CD1d

The crosstalk between the immune and neuroendocrine systems is critical for intestinal homeostasis and gut-brain communications. However, it remains unclear how immune cells participate in gut sensation of hormones and neurotransmitters release in response to environmental cues, such as self-lipids and microbial lipids. We show here that lipid-mediated engagement of invariant natural killer T (iNKT) cells with enterochromaffin (EC) cells, a subset of intestinal epithelial cells, promoted peripheral serotonin (5-HT) release via a CD1d-dependent manner, regulating gut motility and hemostasis. We also demonstrated that inhibitory sphingolipids from symbiotic microbe Bacteroides fragilis represses 5-HT release. Mechanistically, CD1d ligation on EC cells transduced a signal and restrained potassium conductance through activation of protein tyrosine kinase Pyk2, leading to calcium influx and 5-HT secretion. Together, our data reveal that by engaging with iNKT cells, gut chemosensory cells selectively perceive lipid antigens via CD1d to control 5-HT release, modulating intestinal and systemic homeostasis.

ANTIDEPRESSANT MEDICATIONS ARE ASSOCIATED WITH INCREASED RISK OF HOSPITAL-ACQUIRED CLOSTRIDIOIDES DIFFICILE INFECTION: A POPULATION-BASED STUDY

WHAT IS ALREADY KNOWN

•The rate and severity of Clostridioides difficile infection (CDI) has increased throughout North America, the United Kingdom, and Europe. •Scattered evidence about the association of CDI with antidepressant medications use exists in the literature so far. What are the new findings: •The risk of Clostridioides difficile infection is higher in patients who are on mirtazapine, nortriptyline, or trazodone. •The prevalence rate of Clostridioides difficile infection in patients who were using antidepressant medications and the ones who did not, increased with age. Background - During the past decade, Clostridioides difficile infection (CDI) has become the most common cause of antibiotic-associated diarrhea. Several risk factors have been implicated. Scattered evidence about the association of CDI with antidepressant medications use exists in the literature so far. Therefore, we aim to investigate whether the risk of developing CDI is increased in hospitalized patients using antidepressant medications.Methods - Patients who were hospitalized were included in our cohort. We excluded individuals aged less than 18 years. A multivariate regression analysis was performed to calculate the risk of CDI accounting for potential confounders. Results - The risk of CDI in hospitalized patients was increased in individuals diagnosed with inflammatory bowel disease (OR: 4.44; 95%CI: 4.35-4.52), and in patients using clindamycin (OR: 1.55; 95%CI: 1.53-1.57), beta-lactam antibiotics (OR: 1.62; 95%CI: 1.60-1.64), PPI (OR: 3.27; 95%CI: 3.23-3.30), trazodone (OR: 1.31; 95%CI: 1.29-1.33), nortriptyline (OR: 1.25; 95%CI: 1.21-1.28), and mirtazapine (OR: 2.50; 95%CI: 2.46-2.54). After controlling for covariates, the risk of CDI was not increased in patients who were taking fluoxetine (OR: 0.94; 95%CI: 0.92-0.96). Conclusion - In contrary to fluoxetine; mirtazapine, nortriptyline, and trazodone were associated with increased risk of CDI in hospitalized patients.

Gut Microbiota-Derived Short-Chain Fatty Acids: Novel Regulators of Intestinal Serotonin Transporter

Serotonin (5-HT) is a key neurotransmitter synthesized both in the gut and the central nervous system. It exerts its signaling through specific receptors (5-HTR), which regulate numerous behaviors and functions such as mood, cognitive function, platelet aggregation, gastrointestinal motility, and inflammation. Serotonin activity is determined mainly by the extracellular availability of 5-HT, which is controlled by the serotonin transporter (SERT). Recent studies indicate that, by activation of innate immunity receptors, gut microbiota can modulate serotonergic signaling by SERT modulation. As part of its function, gut microbiota metabolize nutrients from diet to produce different by-products, including short-chain fatty acids (SCFAs): propionate, acetate, and butyrate. However, it is not known whether these SCFAs regulate the serotonergic system. The objective of this study was to analyze the effect of SCFAs on the gastrointestinal serotonergic system using the Caco-2/TC7 cell line that expresses SERT and several receptors constitutively. Cells were treated with different SCFAs concentrations, and SERT function and expression were evaluated. In addition, the expression of 5-HT receptors 1A, 2A, 2B, 3A, 4, and 7 was also studied. Our results show that the microbiota-derived SCFAs regulate intestinal serotonergic system, both individually and in combination, modulating the function and expression of SERT and the 5-HT1A, 5-HT2B, and 5-HT7 receptors expression. Our data highlight the role of gut microbiota in the modulation of intestinal homeostasis and suggest microbiome modulation as a potential therapeutic treatment for intestinal pathologies and neuropsychiatric disorders involving serotonin.

The Immune Landscape and Molecular Subtypes of Pediatric Crohn's Disease: Results from In Silico Analysis

Pediatric Crohn's disease (CD) presents a distinct phenotype from adult-onset disease. A dysregulated immune response is critical in CD pathogenesis; thus, it is clinically important to describe immune cell alterations and to identify a new molecular classification for pediatric CD. To this end, in this study, a RNA-seq derived dataset GSE101794-which contains the expression profiles of 254 treatment-naïve pediatric CD samples, including CIBERSORTx and weighted gene-co-expression network analysis (WGCNA)-were performed to estimate the ratio of immune cells and to identify modules and genes related to specific immune cell infiltration, respectively. Hub genes derived from WGCNA were further employed to create a molecular classification using unsupervised K-means clustering. In the pediatric CD samples, it was found that M2 macrophages, CD4⁺ memory resting T cells, CD8⁺ T cells, and resting mast cells were the most prominent immune cells in intestinal tissues. Then, 985 up-regulated genes and 860 down-regulated genes were identified in samples with high immune cell infiltration. Of these differential genes, 10 hub genes (APOA1, CYB5A, XPNPEP2, SLC1A7, SLC4A6, LIPE, G6PC, AGXT2, SLC13A1, and SOAT2) were associated with CD8⁺T cell infiltration. Clinically, the higher expression of these 10 hub genes was strongly associated with an earlier age of CD onset and colonic-type CD. Furthermore, based on these key genes, pediatric CD could be classified into three molecular subtypes, displaying a different immune landscape. Altogether, this in silico analysis provides a novel insight into the immune signature of pediatric CD, and a new classification of pediatric CD is presented, which may help us develop more personalized disease management and treatments for pediatric CD.

Comprehensive protocols for culturing and molecular biological analysis of IBD patient-derived colon epithelial organoids

There are many unanswered questions regarding responses to proinflammatory signals in intestinal epithelial cells (IECs). For example, chemokines secreted by IECs upon external stimuli play multifunctional roles in both homeostasis and during inflammation. Several chemokines are upregulated during active inflammatory bowel disease (IBD), which is associated with an increased influx of immune cells into the gut mucosa. Therefore, studies on how chemokines are regulated in the intestinal epithelium may identify putative treatment targets in IBD. More recently, patient-derived ex vivo models such as intestinal organoids have facilitated molecular analysis of epithelial alterations in IBD patients own cells. Here, we describe refined experimental protocols and methods for the generation and maintenance of IBD patient-derived colonic organoids (colonoids) culture. We also give detailed description of medium, and supplements needed for colonoid establishment, growth, and differentiation, including production of Wnt-3A and Rspondin1 enriched media. Further, we present protocols for RNA and protein isolation from human colonoids, and subsequent gene expression analysis and Western blotting for e.g., signal transduction studies. We also describe how to process colonoids for chemokine protein expression analysis such as immunostaining, confocal imaging, and detection of secreted chemokines by e.g., enzyme-linked immunosorbent assay (ELISA). As proof of principle, we give examples of how the chemoattractant CCL20 can be regulated and expressed in colonoids derived from IBD-patients and healthy controls upon ligands-driven inflammation.

Rooibos (Aspalathus linearis) alters secretome trace amine profile of probiotic and commensal microbes in vitro

ETHNOPHARMACOLOGY RELEVANCE

Aspalathus linearis (Burm.f.) R. Dahlgren (rooibos) tea is anecdotally renowned for its calming effect in the context of gastrointestinal discomfort, but little scientific support is available to elucidate potential mechanisms of action. Enhancement of dietary polyphenol content to improve gut health via prebiotic-like modulation of the gut microbiota has gained significant research interest. Given the known high polyphenol content of rooibos, rooibos tea may potentially exert a prebiotic effect in the gut to facilitate an improvement in chronic inflammatory gastrointestinal conditions.

AIM OF THE STUDY

This study aimed to determine the prebiotic or health-modulating potential of rooibos tea in terms of its effect on gut microbial growth and secretome trace amine composition, as well as to determine how differential rooibos processing alters this activity.

METHODS

Three rooibos preparations (green and fermented leave aqueous extracts, as well as a green leaf ethanol extract) were compared in terms of their phenolic composition (qTOF-LC/MS). Moreover, the effect of rooibos exposure on growth and secretome trace amine levels of probiotic and commensal microbes were assessed (LC/MS). In addition, given the known female bias prevalent for many gastrointestinal disorders, experiments were conducted in the absence and presence of estradiol.

RESULTS

Polyphenolic composition of rooibos was drastically reduced by fermentation. Aqueous extracts of both green and fermented rooibos improved microbial growth, although fermented rooibos had the most pronounced effect (p < 0.01). In terms of secretome trace amine profile, both aqueous extracts of rooibos seemed to facilitate increased putrescine secretion (p < 0.0001) and decreased tryptamine production (p < 0.0001). Estradiol seemed to suppress trace amine secretion by bacteria (Lactobacillus plantarum, Lactobacillus reuteri and Enterococcus mundtii) but increased it in yeast (Saccharomyces boulardii).

CONCLUSION

Rooibos altered gut probiotic and commensal microbial growth and secretome trace amine profiles in vitro, suggesting it has potential to modulate gut microbial composition and functionality as a prebiotic. Current data suggest that these effects are highly dependent on raw material processing. Finally, rooibos may be able to prevent estradiol-associated alterations in trace amine profile, which may have important implications for patient management in female-predominant gastrointestinal disorders.

The Role of Brain-Derived Neurotrophic Factor in Immune-Related Diseases: A Narrative Review

Brain-derived neurotrophic factor (BDNF) is a neurotrophin regulating synaptic plasticity, neuronal excitability, and nociception. It seems to be one of the key molecules in interactions between the central nervous system and immune-related diseases, i.e., diseases with an inflammatory background of unknown etiology, such as inflammatory bowel diseases or rheumatoid arthritis. Studies show that BDNF levels might change in the tissues and serum of patients during the course of these conditions, e.g., affecting cell survival and modulating pain severity and signaling pathways involving different neurotransmitters. Immune-related conditions often feature psychiatric comorbidities, such as sleep disorders (e.g., insomnia) and symptoms of depression/anxiety; BDNF may be related as well to them as it seems to exert an influence on sleep structure; studies also show that patients with psychiatric disorders have decreased BDNF levels, which increase after treatment. BDNF also has a vital role in nociception, particularly in chronic pain, hyperalgesia, and allodynia, participating in the formation of central hypersensitization. In this review, we summarize the current knowledge on BDNF's function in immune-related diseases, sleep, and pain. We also discuss how BDNF is affected by treatment and what consequences these changes might have beyond the nervous system.

Biomarkers for the Evaluation of Pouch Inflammation: A Systematic Review

Background

Ileal pouch inflammation is a common problem following ileal pouch-anal anastomosis (IPAA). Despite its prevalence, diagnosis remains multimodal and requires endoscopy. The use of biomarkers in the prediction of and/or association with pouchitis has not been well characterized. We performed a systematic review to summarize the available evidence.

Method

A search of Ovid, MEDLINE, Cochrane Library, EMBASE, and Web of Science was conducted. Inclusion criteria included studies evaluating biomarkers for the evaluation and prediction of inflammation in patients with IPAA utilizing pouchoscopy as the gold standard. Exclusion criteria included studies on the role of the microbiome or genetic markers.

Results

A total of 28 studies, 5 case-control studies, and 23 observational cohort studies were identified. Fecal biomarkers were assessed in 23 studies, of which fecal calprotectin was the most commonly studied with sensitivities ranging from 57% to 92% and specificities from 19% to 92%. Six studies examined serum biomarkers. None of the serum biomarkers demonstrated a high sensitivity or specificity in association with pouch inflammation. Six studies described the longitudinal assessment of biomarkers. Of these studies, only three reported a predictive role of biomarkers in diagnosing endoscopic inflammation.

Conclusions

Biomarkers have emerged as a potential option to improve the management of pouchitis given the relative ease of sampling compared to pouchoscopy. Unfortunately, the evaluated biomarkers have not consistently demonstrated accuracy in predicting inflammation. Moreover, these biomarkers have not been reliably shown to be sensitive or specific in association with endoscopic pouch inflammation to merit their widespread use in clinical practice.

Comparison of Metabolites and Gut Microbes between Patients with Ulcerative Colitis and Healthy Individuals for an Integrative Medicine Approach to Ulcerative Colitis—A Pilot Observational Clinical Study (STROBE Compliant)

Ulcerative colitis (UC) is an intractable disease associated with high morbidity and healthcare costs. Metabolites and gut microbes are areas of interest for mainstream and complementary and alternative medicine. We, therefore, aimed to contribute to the discovery of an integrative medicine for UC by comparing and analyzing gut microbes and metabolites in patients with UC and in healthy individuals. This was an observational case-control study. Blood and stool samples were collected from the participants, and metabolite and gut microbial studies were performed. Among metabolites, formate, glycolate, trimethylamine, valine, and pyruvate levels were significantly different between the two groups. Among gut microbes, the abundance of Bacteroidetes at the phylum level; Bacteroidia at the class level; Bacteroidales and Actinomycetales at the order level; Prevotellaceae, Acidaminococcaceae, and Leptotrichiaceae at the family level; and Prevotella, Roseburia, Paraprevotella, Phascolarctobacterium, Ruminococcus, Coprococcus, Clostridium_XIVB, Atopobium, and Leptotrichia at the genus level was also significantly different. Most of the metabolites and gut microbes significantly different between the two groups were involved in energy metabolism and inflammatory processes, respectively. The results of this study could be helpful for the identification of targets for integrative medicine approaches for UC.

Effects of Milk-Derived Extracellular Vesicles on the Colonic Transcriptome and Proteome in Murine Model

Evidence shows that effective nutritional intervention can prevent or mitigate the risk and morbidity of inflammatory bowel disease (IBD). Bovine milk extracellular vesicles (mEVs), a major bioactive constituent of milk, play an important role in maintaining intestinal health. The aims of this study were to assess the effects of mEV pre-supplementation on the colonic transcriptome and proteome in dextran sulphate sodium (DSS)-induced acute colitis, in order to understand the underlying molecular mechanisms of mEV protection against acute colitis. Our results revealed that dietary mEV supplementation alleviated the severity of acute colitis, as evidenced by the reduced disease activity index scores, histological damage, and infiltration of inflammatory cells. In addition, transcriptome profiling analysis found that oral mEVs significantly reduced the expression of pro-inflammatory cytokines (IL-1β, IL-6, IL-17A and IL-33), chemokine ligands (CXCL1, CXCL2, CXCL3, CXCL5, CCL3 and CCL11) and chemokine receptors (CXCR2 and CCR3). Moreover, oral mEVs up-regulated 109 proteins and down-regulated 150 proteins in the DSS-induced murine model, which were involved in modulating amino acid metabolism and lipid metabolism. Collectively, this study might provide new insights for identifying potential targets for the therapeutic effects of mEVs on colitis.

Profound gene expression changes in the epithelial monolayer of active ulcerative colitis and Crohn's disease

In recent years it has become apparent that the epithelium is highly involved in inflammatory bowel disease (IBD) pathophysiology. The majority of gene expression studies of IBD are generated from heterogeneous biopsies, providing no distinction between immune cells, the epithelium and other mucosal cells. By using laser capture microdissection (LCM) coupled with RNA sequencing, we aimed to characterize the expressional changes of the isolated colonic epithelial monolayer from ulcerative colitis (UC) and Crohn’s disease (CD) patients compared to healthy controls (HC). The analysis identified 3706 genes as differentially expressed between active IBD epithelium and HC. Weighted gene co-expression network analysis was used to stratify genes into modules, which were subsequently characterized using enrichment analysis. Our data show a distinct upregulation of the antigen presentation machinery during inflammation, including major histocompatibility complex class II molecules (e.g. HLA-DPA1, HLA-DPB1, HLA-DRA) and key transcription factors/activators (STAT1, IRF1, CIITA). We also see an epithelial downregulation of retinoic acid-responsive nuclear receptors (RARA, RARB, RXRA), but upregulation of retinoid-metabolizing enzymes (RDH11, ALDH1A2, ALDH1A3), which together suggest a perturbation of epithelial vitamin A signaling during active IBD. Lastly, we identified a cluster of stress-related genes, including activator protein 1 components JUNB and ATF3, as significantly upregulated in active UC but not in CD, revealing an interesting aspect of IBD heterogeneity. The results represent a unique resource for enhanced understanding of epithelial involvement in IBD inflammation and is a valuable tool for further studies on these processes.

Supplementation with Milk-Derived Extracellular Vesicles Shapes the Gut Microbiota and Regulates the Transcriptomic Landscape in Experimental Colitis

Harboring various proteins, lipids, and RNAs, the extracellular vesicles (EVs) in milk exert vital tissue-specific immune-protective functions in neonates via these bioactive cargos. This study aims to explore the anti-inflammatory effects of bovine milk-derived EVs on a dextran sulfate sodium (DSS)-induced colitis model and to determine the underlying molecular mechanisms. Sixty C57BL/6 mice were divided into the NC group (normal control), DSS group (DSS + PBS), DSS + LOW group (DSS + 1.5 × 10⁸ p/g EVs), DSS + MID group (DSS + 1.5 × 10⁹ p/g EVs), and DSS + HIG group (DSS + 1.0 × 10¹⁰ p/g EVs). Histopathological sections, the gut microbiota, and intestinal tissue RNA-Seq were used to comprehensively evaluate the beneficial functions in mitigating colitis. The morphology exhibited that the milk-derived EVs contributed to the integrity of the superficial epithelial structure in the intestine. Additionally, the concentrations of IL-6 and TNF-α in the colon tissues were significantly decreased in the EVs-treated mice. The abundances of the Dubosiella, Bifidobacterium, UCG-007, Lachnoclostridium, and Lachnospiraceae genera were increased in the gut after treatment with the milk-derived EVs. Additionally, the butyrate and acetate production were enriched in feces. In addition, 1659 genes were significantly down-regulated and 1981 genes were significantly up-regulated in the EVs-treated group. Meanwhile, 82 lncRNAs and 6 circRNAs were also differentially expressed. Overall, the milk-derived EVs could attenuate colitis through optimizing gut microbiota abundance and by manipulating intestinal gene expression, implying their application potential for colitis prevention.

Role of Serotonin in the Maintenance of Inflammatory State in Crohn’s Disease

Crohn’s disease (CD) is a chronic intestinal inflammation considered to be a major entity of inflammatory bowel diseases (IBDs), affecting different segments of the whole gastrointestinal tract. Peripheral serotonin (5-HT), a bioactive amine predominantly produced by gut enterochromaffin cells (ECs), is crucial in gastrointestinal functions, including motility, sensitivity, secretion, and the inflammatory response. These actions are mediated by a large family of serotonin receptors and specialized serotonin transporter (SERT) located on a variety of cell types in the gut. Several studies indicate that intestinal 5-HT signaling is altered in patients with inflammatory bowel disease. Paraformaldehyde-fixed intestinal tissues, obtained from fifteen patients with Crohn’s disease were analyzed by immunostaining for serotonin, Langerin/CD207, and alpha-Smooth Muscle Actin (α-SMA). As controls, unaffected (normal) intestinal specimens of seven individuals were investigated. This study aimed to show the expression of serotonin in dendritic cells (DCs) and myofibroblast which have been characterized with Langerin/CD207 and α-SMA, respectively; furthermore, for the first time, we have found the presence of serotonin in goblet cells. Our results show the correlation between different types of intestinal cells in the maintenance of the inflammatory state in CD linked to the recall of myofibroblasts.

Localization of the Serotonin Transporter in the Dog Intestine and Comparison to the Rat and Human Intestines

Serotonin is crucial in gastrointestinal functions, including motility, sensitivity, secretion, and the inflammatory response. The serotonin transporter (SERT), responsible for serotonin reuptake and signaling termination, plays a prominent role in gastrointestinal physiology, representing a promising therapeutic target in digestive disorders. Serotonin transporter expression has been poorly investigated in veterinary medicine, under both healthy and pathological conditions, including canine chronic enteropathy, in which the serotonin metabolism seems to be altered. The aim of the present study was to determine the distribution of SERT immunoreactivity (SERT-IR) in the dog intestine and to compare the findings with those obtained in the rat and human intestines. Serotonin transporter-IR was observed in canine enterocytes, enteric neurons, lamina propria cells and the tunica muscularis. Data obtained in dogs were consistent with those obtained in rats and humans. Since the majority of the serotonin produced by the body is synthesized in the gastrointestinal tract, SERT-expressing cells may exert a role in the mechanism of serotonin reuptake.

The In Vitro Anti-Inflammatory Activities of Galangin and Quercetin towards the LPS-Injured Rat Intestinal Epithelial (IEC-6) Cells as Affected by Heat Treatment

Flavonols possess several beneficial bioactivities in vitro and in vivo. In this study, two flavonols galangin and quercetin with or without heat treatment (100 °C for 15-30 min) were assessed for their anti-inflammatory activities in lipopolysaccharide (LPS)-stimulated rat intestinal epithelial (IEC-6) cells and whether the heat treatment caused activity changes. The flavonol dosages of 2.5-20 μmol/L had no cytotoxicity on the cells but could enhance cell viability (especially using 5 μmol/L flavonol dosage). The flavonols could decrease the production of prostaglandin E2 and three pro-inflammatory cytokines interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α, and simultaneously promote the production of two anti-inflammatory cytokines IL-10 and transforming growth factor-β. The Western-blot results verified that the flavonols could suppress the LPS-induced expression of TLR4 and phosphorylated IκBα and p65, while the molecular docking results also illustrated that the flavonols could bind with TLR4 and NF-κB to yield energy decreases of -(21.9-28.6) kJ/mol. Furthermore, an inhibitor BAY 11-7082 blocked the NF-κB signaling pathway by inhibiting the expression of phosphorylated IκBα/p65 and thus mediated the production of IL-6/IL-10 as the flavonols did, which confirmed the assessed anti-inflammatory effect of the flavonols. Consistently, galangin had higher anti-inflammatory activity than quercetin, while the heated flavonols (especially those with longer heat time) were less active than the unheated counterparts to exert these target anti-inflammatory effects. It is highlighted that the flavonols could antagonize the LPS-caused IEC-6 cells inflammation via suppressing TLR4/NF-κB activation, but heat treatment of the flavonols led to reduced anti-inflammatory efficacy.

Crosstalk Between Intestinal Serotonergic System and Pattern Recognition Receptors on the Microbiota-Gut-Brain Axis

Disruption of the microbiota-gut-brain axis results in a wide range of pathologies that are affected, from the brain to the intestine. Gut hormones released by enteroendocrine cells to the gastrointestinal (GI) tract are important signaling molecules within this axis. In the search for the language that allows microbiota to communicate with the gut and the brain, serotonin seems to be the most important mediator. In recent years, serotonin has emerged as a key neurotransmitter in the gut-brain axis because it largely contributes to both GI and brain physiology. In addition, intestinal microbiota are crucial in serotonin signaling, which gives more relevance to the role of the serotonin as an important mediator in microbiota-host interactions. Despite the numerous investigations focused on the gut-brain axis and the pathologies associated, little is known regarding how serotonin can mediate in the microbiota-gut-brain axis. In this review, we will mainly discuss serotonergic system modulation by microbiota as a pathway of communication between intestinal microbes and the body on the microbiota-gut-brain axis, and we explore novel therapeutic approaches for GI diseases and mental disorders.

Tryptophan-derived serotonin-kynurenine balance in immune activation and intestinal inflammation

Endogenous tryptophan metabolism pathways lead to the production of serotonin (5‐hydroxytryptamine; 5‐HT), kynurenine, and several downstream metabolites which are involved in a multitude of immunological functions in both health and disease states. Ingested tryptophan is largely shunted to the kynurenine pathway (95%) while only minor portions (1%–2%) are sequestered for 5‐HT production. Though often associated with the functioning of the central nervous system, significant production of 5‐HT, kynurenine and their downstream metabolites takes place within the gut. Accumulating evidence suggests that these metabolites have essential roles in regulating immune cell function, intestinal inflammation, as well as in altering the production and suppression of inflammatory cytokines. In addition, both 5‐HT and kynurenine have a considerable influence on gut microbiota suggesting that these metabolites impact host physiology both directly and indirectly via compositional changes. It is also now evident that complex interactions exist between the two pathways to maintain gut homeostasis. Alterations in 5‐HT and kynurenine are implicated in the pathogenesis of many gastrointestinal dysfunctions, including inflammatory bowel disease. Thus, these pathways present numerous potential therapeutic targets, manipulation of which may aid those suffering from gastrointestinal disorders. This review aims to update both the role of 5‐HT and kynurenine in immune regulation and intestinal inflammation, and analyze the current knowledge of the relationship and interactions between 5‐HT and kynurenine pathways.

The Multifaceted Role of Serotonin in Intestinal Homeostasis

The monoamine serotonin, 5-hydroxytryptamine (5-HT), is a remarkable molecule with conserved production in prokaryotes and eukaryotes and a wide range of functions. In the gastrointestinal tract, enterochromaffin cells are the most important source for 5-HT production. Some intestinal bacterial species are also able to produce 5-HT. Besides its role as a neurotransmitter, 5-HT acts on immune cells to regulate their activation. Several lines of evidence indicate that intestinal 5-HT signaling is altered in patients with inflammatory bowel disease. In this review, we discuss the current knowledge on the production, secretion, and signaling of 5-HT in the intestine. We present an inventory of intestinal immune and epithelial cells that respond to 5-HT and describe the effects of these signaling processes on intestinal homeostasis. Further, we detail the mechanisms by which 5-HT could affect inflammatory bowel disease course and describe the effects of interventions that target intestinal 5-HT signaling.

Nano-analysis reveals high fraction of serotonin release during exocytosis from a gut epithelium model cell

Electrochemical methods were used to explore the exocytotic nature of serotonin (5‐HT) release in human carcinoid BON cells, an in vitro human enterochromaffin cell model, to understand the mechanisms operating the release of gut‐derived 5‐HT in the intestinal mucosal epithelium. We show that the fractional vesicular 5‐HT release in BON cells is 80 % compared to previous work in pancreatic beta cells (34 %). The fractional release increased from 80 % in control BON cells to 87 % with 5‐HT preincubation and nearly 100 % with the combination of 5‐HT and the 5‐HT₄ autoreceptor agonist, cisapride. Thus, partial release is the primary mechanism of exocytosis in BON cells, resulting in a variable amount of the vesicular content being released. Factors that control secretion of 5‐HT from enterochromaffin cells or BON cells are important as partial release provides a mechanism for development of effective therapeutic strategies to treat gastrointestinal diseases.

Tryptophan metabolites modulate inflammatory bowel disease and colorectal cancer by affecting immune system

Tryptophan is an essential amino acid, going through three different metabolic pathways in the intestines. Indole pathway in the gut microbiota, serotonin system in the enterochromaffin cells and kynurenine pathway in the immune cells and intestinal lining are the three arms of tryptophan metabolism in the intestines. Clinical, in vivo and in vitro studies showed that each one of these arms has a significant impact on IBD. This review explains how different metabolites of tryptophan are involved in the pathophysiology of IBD and colorectal cancer, as a major complication of IBD. Indole metabolites alleviate colitis and protect against colorectal cancer while serotonin arm follows a more complicated and receptor-specific pattern. Indole metabolites and kynurenine interact with aryl hydrocarbon receptor (AHR) to induce T regulatory cells differentiation, confine Th17 and Th1 response and produce anti-inflammatory mediators. Kynurenine decreases tumor-infiltrating CD8+ cells and mediates tumor cells immune evasion. Serotonin system also increases colorectal cancer cells proliferation and metastasis while, indole metabolites can profoundly decrease colorectal cancer growth. Targeted therapy for tryptophan metabolites may improve the management of IBD and colorectal cancer, e.g. supplementation of indole metabolites such as indole-3-carbinol (I3C), inhibition of kynurenine monooxygenase (KMO) and selective stimulation or inhibition of specific serotonergic receptors can mitigate colitis. Furthermore, it will be explained how indole metabolites supplementation, inhibition of indoleamine 2,3-dioxygenase 1 (IDO1), KMO and serotonin receptors can protect against colorectal cancer. Additionally, extensive molecular interactions between tryptophan metabolites and intracellular signaling pathways will be thoroughly discussed.

Overproduction of Gastrointestinal 5-HT Promotes Colitis-Associated Colorectal Cancer Progression via Enhancing NLRP3 Inflammasome Activation

Chronic inflammation is a key driver for colitis-associated colorectal cancer. 5-hydroxytryptamine (5-HT), a neurotransmitter, has been reported to promote inflammation in the gastrointestinal tract. However, the mechanism behind this remains unclear. In this study, we found that 5-HT levels, as well as the expression of tryptophan hydroxylase 1 (TPH1), the 5-HT biosynthesis rate-limiting enzyme, were significantly upregulated in colorectal tumor tissues from patients with colorectal cancer, colorectal cancer mouse models, and colorectal cancer cell lines when compared with normal colorectal tissues or epithelial cell lines. Colorectal cancer cell-originated 5-HT enhanced NLRP3 inflammasome activation in THP-1 cells and immortalized bone marrow-derived macrophages (iBMDM) via its ion channel receptor, HTR3A. Mechanistically, HTR3A activation led to Ca²⁺ influx, followed by CaMKIIα phosphorylation (Thr286) and activation, which then induced NLRP3 phosphorylation at Ser198 (mouse: Ser194) and inflammasome assembling. The NLRP3 inflammasome mediated IL1β maturation, and release upregulated 5-HT biosynthesis in colorectal cancer cells by inducing TPH1 transcription, revealing a positive feedback loop between 5-HT and NLRP3 signaling. Silencing TPH1 or HTR3A by short hairpin RNA slowed down tumor growth in an established CT26 and iBMDM coimplanted subcutaneous allograft colorectal cancer mouse model, whereas treatment with TPH1 inhibitor 4-chloro-DL-phenylalanine or HTR3A antagonist tropisetron alleviated tumor progression in an azoxymethane/dextran sodium sulfate-induced colorectal cancer mouse model. Addressing the positive feedback loop between 5-HT and NLRP3 signaling could provide potential therapeutic targets for colorectal cancer.

Serotonin in the Pathogenesis of Lymphocytic Colitis

Lymphocytic colitis (LC) is a chronic inflammatory disease associated with watery diarrhea, abdominal pain, and colonic intraepithelial lymphocytosis. Serotonin (5-hydroxytryptamine, 5-HT) is reported to increase in certain colon diseases; however, little is known regarding its metabolism in LC. In the present work, the level of 5-HT in serum and the number of enteroendocrine cells (EECs) as well as the expression of the 5-HT rate-limiting enzyme tryptophan hydroxylase 1 (TPH1) in colonic biopsies and urine 5-hydroxyindoeoacetic acid (5-HIAA) were determined in 36 LC patients that were treated with budesonide and 32 healthy controls. The 5-HT serum and 5-HIAA urine levels were measured using ELISA, the EEC number was determined immunohistochemically, and the colonic TPH1 mRNA expression was determined using RT-PCR. The levels of 5-HT and 5-HIAA and the number of EECs were higher in LC patients than in the controls, and positive correlations were observed between the 5-HT and 5-HIAA levels, 5-HT and EEC number, TPH1 mRNA and EEC number, as well as the severity of disease symptoms and 5-HIAA. Budesonide decreased the levels of 5-HT, 5-HIAA, and TPH1 expression and the number of EECs to values that did not differ from those for controls. In conclusion, the serotonin metabolism may be important for LC pathogenesis, and the urinary level of 5-HIAA may be considered as a non-invasive marker of this disease activity.