Serotonin Modulates AhR Activation by Interfering with CYP1A1-Mediated Clearance of AhR Ligands.

BACKGROUND/AIMS: Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter and hormone with important physiological functions in many organs, including the intestine. We have previously shown that 5-HT activates the aryl hydrocarbon receptor (AhR) in intestinal epithelial cells (IECs) via a serotonin transporter (SERT)-dependent mechanism. AhR is a nuclear receptor that binds a variety of molecules including tryptophan (TRP) metabolites to regulate physiological processes in the intestine including xenobiotic detoxification and immune modulation. We hypothesized that 5-HT activates AhR indirectly by interfering with metabolic clearance of AhR ligands by cytochrome P450 1A1 (CYP1A1). METHODS: Inhibition of CYP1A1 activity by 5-HT was assessed in the human intestinal epithelial cell line Caco-2 and recombinant CYP1A1 microsomes using both luciferase and LC-MS/MS. Degradation of 5-HT by recombinant CYP1A1 was measured by LC-MS/MS. For in vitro studies, CYP1A1 and CYP1B1 mRNA expression levels were measured by RT-PCR and CYP1A1 activity was measured by ethoxyresorufin-O-deethylase (EROD) assays. For in vivo studies, AhR ligands were administered to SERT KO mice and WT littermates and intestinal mucosa CYP1A1 mRNA was measured. RESULTS: We show that 5-HT inhibits metabolism of both the pro-luciferin CYP1A1 substrate Luc-CEE as well as the high affinity AhR ligand 6-formylindolo[3,2-b] carbazole (FICZ). Recombinant CYP1A1 assays revealed that 5-HT is metabolized by CYP1A1 in an NADPH dependent manner. Treatment with 5-HT in TRP-free medium, which is devoid of trace AhR ligands, showed that 5-HT requires the presence of AhR ligands to activate AhR. Cotreatment with 5-HT and FICZ confirmed that 5-HT potentiates induction of AhR target genes by AhR ligands. However, this was only true for ligands which are CYP1A1 substrates such as FICZ. Administration of ß-napthoflavone by gavage or indole-3-carbinol via diet to SERT KO mice revealed that lack of SERT impairs intestinal AhR activation. CONCLUSION: Our studies provide novel evidence of crosstalk between serotonergic and AhR signaling where 5-HT can influence the ability of AhR ligands to activate the receptor in the intestine.

Assessment of the Degree of Variation of Histologic Inflammation in Ulcerative Colitis.

INTRODUCTION: Treatment of ulcerative colitis (UC) now includes mucosal healing. Adoption of histologic end points is hindered by a lack of evidence guiding optimal sampling, interpretation, and reproducibility of results. METHODS: We analyzed biopsy fragments from colonoscopies in 92 patients with UC. Fragments were scored using 6-point histologic inflammatory activity (HIA) scale. Variability was determined using ordinal representations of HIA scores. The most frequently observed score and percentage of biopsy fragments with that score were determined for each biopsy, each segment, and across all 3 segments for each colonoscopy. Mean percentages and 95% confidence intervals (CIs) were calculated. RESULTS: We reviewed 1802 biopsy fragments. The mean percentages of intrasegment biopsy fragments with the same HIA score were 85.5% (95% CI, 80.9% to 92.9%), 79.6% (95% CI, 76.0% to 87.3%), and 82.7% (95% CI, 79.1% to 90.0%) for the rectum, left colon, and right colon, respectively. The mean percentage of intersegment biopsy fragments with the same HIA score was 70.2% (95% CI, 65.7% to 82.5%). The mean percentages of intrabiopsy fragments with the same HIA score were 83.3% (95% CI, 77.6% to 93.5%), 83.6% (95% CI, 80.1% to 89.7%), and 90.2% (95% CI, 87.6% to 94.7%) for the rectum, left colon, and right colon, respectively. All 3 analyses revealed increased variation when a greater degree of histologic inflammation was present in the biopsies (mean HIA score ≥2). CONCLUSIONS: We found minimal variability between degree of inflammation among biopsy fragments within and among different colorectal segments in UC, suggesting that even a single biopsy would adequately reflect the inflammation of the entire colorectum. These findings have significant implications for the use of histology as a clinical target and trial end point in UC.

Abdominal pain and fever in a patient with human immunodeficiency virus: a case report.

BACKGROUND: Neutropenic enterocolitis (NE), or typhlitis, a condition typically associated with severe neutropenia in the setting of chemotherapy, is highly morbid (50-100%) and benefits from early diagnosis. It has been associated with neutropenia in the setting of human immunodeficiency virus (HIV) but has not been described in a patient with HIV who was not neutropenic on presentation. We present the case of a patient with HIV who was not neutropenic on presentation but found to have NE. CASE PRESENTATION: A 27-year-old male with a history of HIV on antiretroviral therapy and epilepsy presented with concern for breakthrough seizure. The patient revealed he was having non-bloody, non-bilious emesis and diarrhea for 3 days. Initial labs were white blood cell count 3.9 × 109/L, absolute neutrophil count (ANC) 3.14 × 109/L, CD4 count 290 cells/mm3, and undetectable viral load. A computed tomography (CT) scan of the abdomen/pelvis with contrast revealed wall thickening of the cecum and proximal ascending colon (Fig. 1), suggestive of NE. The patient was started on cefepime and metronidazole but switched to piperacillin/tazobactam after he became leukopenic/neutropenic. CONCLUSIONS: Neutropenic enterocolitis, typically presenting with fever, abdominal pain, and hematochezia, can be difficult to identify, particularly in patients without a history of malignancy. However, it should be considered in patients with HIV presenting with these symptoms, even with a normal ANC and CD4 count above 200 cells/mm3. Prompt diagnosis can be made with CT, and early initiation of broad-spectrum antibiotics greatly reduces the risk of morbidity/mortality.

Enterococcus faecalis Is Associated with Anastomotic Leak in Patients Undergoing Colorectal Surgery.

Background: Anastomotic leak is among the most dreaded complications in patients undergoing colorectal surgery. We have discovered that in rodents, collagenase-producing bacteria, particularly Enterococcus faecalis, promotes anastomotic leak by degrading healing anastomotic tissue. Yet, it is unclear if these organisms play a role in humans. Patients and Methods: Patients undergoing colorectal resection at the University of Chicago from July 2014 through June 2019 who developed a post-operative infection were stratified into infections that resulted from an anastomotic leak, a Hartmann pouch stump leak, or a deep infection without an associated staple line leak. Results: Forty-two patients had available culture data. Of these patients, 19 were found to have an anastomotic leak, 7 had a stump leak, and 16 had a deep infection that was not associated with a staple line. Enterococcus faecalis was identified in 24% of all infections and was associated with the development of anastomotic leak (p = 0.029). When the organisms were classified into their known ability to produce collagenase, 74% of patients with an anastomotic leak were colonized with collagenase-producing organisms, compared with only 28% of patients with a deep infection or stump leak (p = 0.022). Antibiotic-resistant organisms were more common in patients with anastomotic leak (p = 0.01). Conclusions: Collagenase-producing and antibiotic-resistant organisms are more prevalent in anastomotic leak infections compared with other deep or organ/space infections. This lends evidence to a bacterial driven pathogenesis of leak and suggests that targeting these organisms may be a novel strategy to reduce this complication.

Identification of Risk Factors for Coexisting Sinusitis and Inflammatory Bowel Disease.

BACKGROUND: This study aimed to analyze the association of coexisting sinusitis and IBD, establish significant factors involved in their development, and enable further biological correlation between these two diseases. METHODS: The IBD and Sinusitis Study at UChicago Medicine (TISSUe) is a retrospective, single-center study. We reviewed patients to confirm IBD and chronic sinusitis diagnoses. Case-control propensity score matching was performed using matched controls with IBD only or sinusitis only. Statistical methods included Chi-squared test and Wilcoxon rank sum test. Logistic regression analysis was performed, and factors were considered significant if p<0.05. RESULTS: Stratifying 214 patients with coexisting IBD and sinusitis, 176 patients had IBD first and 38 patients had sinusitis first. Multivariable analysis of factors associated with subsequent disease with matched controls determined that duration of disease, UC, steroid exposure ever, and younger age of IBD diagnosis were associated with subsequent sinusitis in patients with IBD; steroid exposure ever and duration of sinusitis were significantly associated with subsequent IBD in patients with sinusitis. CONCLUSIONS: This study suggests that IBD maintenance therapies are not associated with increased risk of sinusitis, as proposed by adverse events in clinical trial data; rather, UC diagnosis and duration of disease may be more influential in sinusitis development. While further studies are necessary, this study also demonstrates that sinusitis precedes IBD in some patients, probing its biological association with IBD and possible classification as an extraintestinal manifestation.

Serotonin transporter untranslated regions influence mRNA abundance and protein expression.

The serotonin transporter (SERT, SLC6A4) is a Na+-dependent transporter that regulates the availability of serotonin (5-HT, 5-hydroxytryptamine), a key neurotransmitter and hormone in the brain and the intestine. The human SERT gene consists of two alternate promoters that drive expression of an identical SERT protein. However, there are different mRNA transcript variants derived from these two promoters that differ in their 5' untranslated region (5'UTR), which is the region of the mRNA upstream from the protein-coding region. Two of these transcripts contain exon-1a and are abundant in neuronal tissue, whereas the third transcript contains exon-1c and is abundant in the intestine. The 3'UTR is nearly identical among the transcripts. Current studies tested the hypothesis that the UTRs of SERT influence its expression in intestinal epithelial cells (IECs) by controlling mRNA or protein levels. The SERT UTRs were cloned into luciferase reporter plasmids and luciferase mRNA and activity were measured following transient transfection of the UTR constructs into the model IEC Caco-2. Luciferase activity and mRNA abundance were higher than the empty vector for two of the three 5'UTR variants. Calculation of translation index (luciferase activity divided by the relative luciferase mRNA level) revealed that the exon-1a containing 5'UTRs had enhanced translation when compared to the exon-1c containing 5'UTR which exhibited a low translation efficiency. Compared to the empty vector, the SERT 3'UTR markedly decreased luciferase activity. In silico analysis of the SERT 3'UTR revealed many conserved potential miRNA binding sites that may be responsible for this decrease. In conclusion, we have shown that the UTRs of SERT regulate mRNA abundance and protein expression. Delineating the molecular basis by which the UTRs of SERT influence its expression will lead to an increased understanding of post-transcriptional regulation of SERT in GI disorders associated with altered 5-HT availability.