OBJECTIVE: The abdominal discomfort experienced by patients with colitis may be attributable in part to the presence of small intestinal dysmotility, yet mechanisms linking colonic inflammation with small-bowel motility remain largely unexplored. We hypothesize that colitis results in small intestinal hypomotility owing to a loss of enteroendocrine cells (EECs) within the small intestine that can be rescued using serotonergic-modulating agents.
METHODS: Male C57BL/6J mice, as well as mice that overexpress (EECOVER) or lack (EECDEL) NeuroD1+ enteroendocrine cells, were exposed to dextran sulfate sodium (DSS) colitis (2.5% or 5% for 7 days) and small intestinal motility was assessed by 70-kilodalton fluorescein isothiocyanate-dextran fluorescence transit. EEC number and differentiation were evaluated by immunohistochemistry, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling staining, and quantitative reverse-transcriptase polymerase chain reaction. Mice were treated with the 5-hydroxytryptamine receptor 4 agonist prucalopride (5 mg/kg orally, daily) to restore serotonin signaling.
RESULTS: DSS-induced colitis was associated with a significant small-bowel hypomotility that developed in the absence of significant inflammation in the small intestine and was associated with a significant reduction in EEC density. EEC loss occurred in conjunction with alterations in the expression of key serotonin synthesis and transporter genes, including Tph1, Ddc, and Slc6a4. Importantly, mice overexpressing EECs revealed improved small intestinal motility, whereas mice lacking EECs had worse intestinal motility when exposed to DSS. Finally, treatment of DSS-exposed mice with the 5-hydroxytryptamine receptor 4 agonist prucalopride restored small intestinal motility and attenuated colitis.
CONCLUSIONS: Experimental DSS colitis induces significant small-bowel dysmotility in mice owing to enteroendocrine loss that can be reversed by genetic modulation of EEC or administering serotonin analogs, suggesting novel therapeutic approaches for patients with symptomatic colitis.

The prevalence of inflammatory bowel disease (IBD) is rising globally; however, its etiology is still not fully understood. Patient genetics, immune system, and intestinal microbiota are considered critical factors contributing to IBD. Preclinical animal models are crucial to better understand the importance of individual contributing factors. Among these, the dextran sodium sulfate (DSS) colitis model is the most widely used. DSS treatment induces gut inflammation and dysbiosis. However, its exact mode of action remains unclear. To determine whether DSS treatment induces pathogenic changes in the microbiota, we investigated the microbiota-modulating effects of DSS on murine microbiota in vitro. For this purpose, we cultured murine microbiota from the colon in six replicate continuous bioreactors. Three bioreactors were supplemented with 1% DSS and compared with the remaining PBS-treated control bioreactors by means of microbiota taxonomy and functionality. Using metaproteomics, we did not identify significant changes in microbial taxonomy, either at the phylum or genus levels. No differences in the metabolic pathways were observed. Furthermore, the global metabolome and targeted short-chain fatty acid (SCFA) quantification did not reveal any DSS-related changes. DSS had negligible effects on microbial functionality and taxonomy in vitro in the absence of the host environment. Our results underline that the DSS colitis mouse model is a suitable model to study host-microbiota interactions, which may help to understand how intestinal inflammation modulates the microbiota at the taxonomic and functional levels.

The study aimed to investigate the potential of low dose chitooligosaccharide (COS) in ameliorating dextran sodium sulfate (DSS) induced chronic colitis by regulating microbial dysbiosis and pro-inflammatory responses. Chronic colitis was induced in BALB/c mice by DSS (4% w/v, 3 cycles of 5 days) administration. The mice were divided into four groups: vehicle, DSS, DSS + mesalamine and DSS+COS. COS and mesalamine were administered orally, daily once, from day 1 to day 30 at a dose of 20 mg/kg and 50 mg/kg respectively. The disease activity index (DAI), colon length, histopathological score, microbial composition, and pro-inflammatory cytokine expression were evaluated. COS (20 mg/kg, COSLow) administration reduced the disease activity index, and colon shortening, caused by DSS significantly. Furthermore, COSLow restored the altered microbiome in the gut and inhibited the elevated pro-inflammatory cytokines (IL-1 and IL-6) in the colon against DSS-induced chronic colitis in mice. Moreover, COSLow treatment improved the probiotic microflora thereby restoring the gut homeostasis. In conclusion, this is the first study where microbial dysbiosis and pro-inflammatory responses were modulated by chronic COSLow treatment against DSS-induced chronic colitis in Balb/c mice. Therefore, COS supplementation at a relatively low dose could be efficacious for chronic inflammatory bowel disease.

Inflammatory bowel disease (IBD) represents a prominent chronic immune-mediated inflammatory disorder, yet its etiology remains poorly comprehended, encompassing intricate interactions between genetics, immunity, and the gut microbiome. This study uncovers a novel colitis-associated risk gene, namely Ring1a, which regulates the mucosal immune response and intestinal microbiota. Ring1a deficiency exacerbates colitis by impairing the immune system. Concomitantly, Ring1a deficiency led to a Prevotella genus-dominated pathogenic microenvironment, which can be horizontally transmitted to co-housed wild type (WT) mice, consequently intensifying dextran sodium sulfate (DSS)-induced colitis. Furthermore, we identified a potential mechanism linking the altered microbiota in Ring1aKO mice to decreased levels of IgA, and we demonstrated that metronidazole administration could ameliorate colitis progression in Ring1aKO mice, likely by reducing the abundance of the Prevotella genus. We also elucidated the immune landscape of DSS colitis and revealed the disruption of intestinal immune homeostasis associated with Ring1a deficiency. Collectively, these findings highlight Ring1a as a prospective candidate risk gene for colitis and suggest metronidazole as a potential therapeutic option for clinically managing Prevotella genus-dominated colitis.
We found that PcG protein Ring1a could be a new risk gene for colitis. Ring1a deficiency causes aggravated colitis by regulating the mucosal immune system and colonic microbial ecology.

Patients with inflammatory bowel disease (IBD) have a higher risk of developing colitis-associated colorectal cancer (CAC) with poor prognosis. IBD etiology remains undefined but involves environmental factors, genetic predisposition, microbiota imbalance (dysbiosis) and mucosal immune defects. Mesenchymal stromal cell (MSC) injections have shown good efficacy in reducing intestinal inflammation in animal and human studies. However, their effect on tumor growth in CAC and their capacity to restore gut dysbiosis are not clear.
The outcome of systemic administrations of in vitro expanded human intestinal MSCs (iMSCs) on tumor growth in vivo was evaluated using the AOM/DSS model of CAC in C57BL/6J mice. Innate and adaptive immune responses in blood, mesenteric lymph nodes (MLNs) and colonic tissue were analyzed by flow cytometry. Intestinal microbiota composition was evaluated by 16S rRNA amplicon sequencing.
iMSCs significantly inhibited colitis and intestinal tumor development, reducing IL-6 and COX-2 expression, and IL-6/STAT3 and PI3K/Akt signaling. iMSCs decreased colonic immune cell infiltration, and partly restored intestinal monocyte homing and differentiation. iMSC administration increased the numbers of Tregs and IFN-γ+CD8+ T cells in the MLNs while decreasing the IL-4+Th2 response. It also ameliorated intestinal dysbiosis in CAC mice, increasing diversity and Bacillota/Bacteroidota ratio, as well as Akkermansia abundance, while reducing Alistipes and Turicibacter, genera associated with inflammation.
Administration of iMSCs protects against CAC, ameliorating colitis and partially reverting intestinal dysbiosis, supporting the use of MSCs for the treatment of IBD.

Inflammation of the GI tract leads to compromised epithelial barrier integrity, which increases intestine permeability. A compromised intestinal barrier is a critical event that leads to microbe entry and promotes inflammatory responses. Inflammatory bowel diseases that comprise Crohn\'s disease (CD) and ulcerative colitis (UC) show an increase in intestinal permeability. Nerolidol (NED), a naturally occurring sesquiterpene alcohol, has potent anti-inflammatory properties in preclinical models of colon inflammation. In this study, we investigated the effect of NED on MAPKs, NF-κB signaling pathways, and intestine epithelial tight junction physiology using in vivo and in vitro models. The effect of NED on proinflammatory cytokine release and MAPK and NF-κB signaling pathways were evaluated using lipopolysaccharides (LPS)-stimulated RAW 264.7 macrophages. Subsequently, the role of NED on MAPKs, NF-κB signaling, and the intestine tight junction integrity were assessed using DSS-induced colitis and LPS-stimulated Caco-2 cell culture models. Our result indicates that NED pre-treatment significantly inhibited proinflammatory cytokine release, expression of proteins involved in MAP kinase, and NF-κB signaling pathways in LPS-stimulated RAW macrophages and DSS-induced colitis. Furthermore, NED treatment significantly decreased FITC-dextran permeability in DSS-induced colitis. NED treatment enhanced tight junction protein expression (claudin-1, 3, 7, and occludin). Time-dependent increases in transepithelial electrical resistance (TEER) measurements reflect the formation of healthy tight junctions in the Caco-2 monolayer. LPS-stimulated Caco-2 showed a significant decrease in TEER. However, NED pre-treatment significantly prevented the fall in TEER measurements, indicating its protective role. In conclusion, NED significantly decreased MAPK and NF-κB signaling pathways and decreased tight junction permeability by enhancing epithelial tight junction protein expression.

Food allergy (FA) has become a global food safety issue. Evidence suggests that inflammatory bowel disease (IBD) can increase the incidence of FA, but it is mostly based on epidemiological studies. An animal model is pivotal for unraveling the mechanisms involved. However, dextran sulfate sodium (DSS)-induced IBD models may cause substantial animal losses. To better investigate the effect of IBD on FA, this study aimed to establish a murine model to fit both IBD and FA symptoms. Firstly, we compared three DSS-induced colitis models by monitoring survival rate, disease activity index, colon length, and spleen index, and then eliminated the colitis model with a 7-day administration of 4% due to high mortality. Moreover, we evaluated the modeling effects on FA and intestinal histopathology of the two models selected and found the modeling effects were similar in both the colitis model with a 7-day administration of 3% DSS and the colitis model with long-term administration of DSS. However, for animal survival reasons, we recommend the colitis model with long-term administration of DSS.

Inflammatory bowel diseases (IBDs) are chronic inflammatory disorders that include Crohn\'s disease (CD) and ulcerative colitis (UC). The incidence of IBD is rising globally. However, the etiology of IBD is complex and governed by multiple factors. The current clinical treatment for IBD mainly includes steroids, biological agents and need-based surgery, based on the severity of the disease. Current drug therapy is often associated with adverse effects, which limits its use. Therefore, it necessitates the search for new drug candidates. In this pursuit, phytochemicals take the lead in the search for drug candidates to benefit from IBD treatment. β-myrcene is a natural phytochemical compound present in various plant species which possesses potent anti-inflammatory activity. Here we investigated the role of β-myrcene on colon inflammation to explore its molecular targets. We used 2% DSS colitis and TNF-α challenged HT-29 adenocarcinoma cells as in vivo and in vitro models. Our result indicated that the administration of β-myrcene in dextran sodium sulfate (DSS)-treated mice restored colon length, decreased disease activity index (DAI), myeloperoxidase (MPO) enzyme activity and suppressed proinflammatory mediators. β-myrcene administration suppressed mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB) pathways to limit inflammation. β-myrcene also suppressed mRNA expression of proinflammatory chemokines in tumor necrosis factor-α (TNF-α) challenged HT-29 adenocarcinoma cells. In conclusion, β-myrcene administration suppresses colon inflammation by inhibiting MAP kinases and NF-κB pathways.

Inflammatory bowel disease (IBD) is a chronic recurrent inflammatory disease with unknown etiology. Dextran sulfate sodium (DSS) induced colitis is a widely used mouse model in IBD research. DSS colitis involves activation of the submucosal immune system and can be used to study IBD-like disease characteristics in acute, chronic, remission and transition phases. Insight into colon inflammatory parameters is needed to understand potentially irreversible adaptations to the chronification of colitis, determining the baseline and impact of further inflammatory episodes. We performed analyses of non-invasive and invasive colitis parameters in acute, chronic and remission phases of the DSS colitis in C57BL/6 mice. Non-invasive colitis parameters poorly reflected inflammatory aspects of colitis in chronic remission phase. We found invasive inflammatory parameters, positively linked to repeated DSS-episodes, such as specific colon weight, inflamed colon area, spleen weight, absolute cell numbers of CD4+ and CD8+ T cells as well as B cells, blood IFN-γ level, colonic chemokines BLC and MDC as well as the prevalence of Turicibacter species in feces. Moreover, microbial Lactobacillus species decreased with chronification of disease. Our data point out indicative parameters of recurrent gut inflammation in context of DSS colitis.

Psoriasis has long been associated with inflammatory bowel disease (IBD); however, a causal link is yet to be established. Here, we demonstrate that imiquimod-induced psoriasis (IMQ-pso) in mice disrupts gut homeostasis, characterized by increased proportions of colonic CX3CR1hi macrophages, altered cytokine production, and bacterial dysbiosis. Gut microbiota from these mice produce higher levels of succinate, which induce de novo proliferation of CX3CR1hi macrophages ex vivo, while disrupted gut homeostasis primes IMQ-pso mice for more severe colitis with dextran sulfate sodium (DSS) challenge. These results demonstrate that changes in the gut environment in psoriasis lead to greater susceptibility to IBD in mice, suggesting a two-hit requirement, that is, psoriasis-induced altered gut homeostasis and a secondary environmental challenge. This may explain the increased prevalence of IBD in patients with psoriasis.