Breen‐Lyles, Margaret K.

Background: Polyamines produced by host cells and intestinal microbiota and are critical to overall health. Studies have shown putrescine, a polyamine, can strengthen, or in some instances disrupt, gastrointestinal (GI) barrier integrity, yet the regulation of polyamine concentrations in the GI tract is unknown. Host colonocytes and microbiota both metabolize polyamines, and in GI diseases like irritable bowel syndrome (IBS) where intestinal microbiota is significantly altered, polyamine metabolism may be affected. Aim: Determine regulation of luminal polyamine concentration and its effects on intestinal barrier integrity. Hypothesis: Luminal polyamine concentration is suppressed by commensal intestinal microbiota and increasing concentration of putrescine results in intestinal barrier disruption. Methods: Microbiota effects on luminal polyamine concentrations were assessed by humanizing germ-free (GF) mice with a single oral gavage of commensal human microbiota. Polyamine effect on barrier integrity was assessed in vitro using Caco-2 cells and ex vivo on Ussing using mouse colonic tissue with 300Da fluorescein and 4kDa FITC-Dextran tracers. Changes in transepithelial resistance (TER) and rate of tracer flux was recorded. Untargeted metabolomics with shotgun metagenomics was completed on human fecal samples and sigmoid colonic biopsies were collected for bulk RNAseq. Bray-Curtis distance was determined at the species level using the PERMANOVA method and used to test relationships between beta-diversity and fecal polyamine concentration. Results: Humanization with human commensal microbiota (1.2% C. aerofaciens) lead to a 20-fold increase in cecal putrescine and a 20-fold decrease in fecal putrescine compared to GF controls. In vitro addition of putrescine (100mM) caused increased fluorescein flux (3.50±0.24 vs 1.44±0.04 mg/mL) and a rapid loss of transepithelial resistance compared to controls (% of Baseline TER, 36.6±8.2 vs 102.8±5.4, 3h postexposure). Ex vivo addition of putrescine caused a loss of TER (57% vs 89% of baseline by 3h) and an increased rate of 4kDa FITC-Dextran flux compared to untreated controls (1236±131 vs 562±70 ng/hr/cm2). Transcriptomic profiles show decreased expression of ornithine decarboxylase antienzyme (OAZ1, FDR=0.018) in IBS which inhibits the rate limiting enzyme for putrescine production. Increased lactulose excretion (2-24h), suggestive of increased distal colonic permeability, correlated with N-acetylputrescine concentration (p=0.07). N-acetylputrescine also correlated positively with increased stool frequency (p=0.009) and looser consistency (p=0.013). C. aerofaciens, a polyamine consumer, negatively correlated with n-acetylputrescine (FDR=0.02) suggesting a loss of specific taxa may lead to insuffcient polyamine metabolism. Conclusion: Polyamines, namely putrescine, disrupts intestinal barrier integrity, correlate with in vivo permeability, and are decreased in the colon by commensal microbiota. These observations identify putrescine as a negative effector of barrier function and suggest a novel role for the commensal microbiome in regulating barrier integrity through polyamine metabolism. Further work investigating host and microbiota mechanisms of polyamine metabolism, signaling and the specific taxa involved is needed to better understand the effects polyamines have on GI physiology. NIH DK 127998 (MG), support from Mayo Clinic Center for Individualized Medicine (CIM), and Mayo Clinic Center for Cell Signalling in Gastroenterology (C-Sig) P30DK084567. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

AbstractBackgroundAnimal models and human data have suggested macrophage‐driven immune dysregulation in diabetic gastroparesis (DG). Translocator protein (TSPO) upregulation has been suggested to indicate activated state of macrophages and ER176 is a high affinity third generation TSPO‐specific radioligand. The aim of this study was to determine feasibility of dynamic 11C‐ER 176 PET to identify macrophage activation in DG.MethodsTwelve patients, all females, were recruited (4 DG, 4 diabetics, and 4 healthy volunteers) for 11C‐ER 176 PET/CT scanning. The standardized uptake value (SUVmax) in the gastric fundus, body, pylorus, and descending part of the duodenum were compared between three groups using Kruskal‐Wallis test to perform the comparisons, and a p‐value of 0.05 was considered statistically significant.Key ResultsAge was comparable among the three groups with a median of 53 years. The uptake was higher in pylorus in diabetics compared to DG and healthy (SUVmax healthy 4.6 ± 0.2, diabetics 8.4 ± 4.1, DG 5.5 ± 1.0, p = 0.04). The uptake was similar in gastric fundus (9.0 ± 1.6, 13.1 ± 8.3, 7.8 ± 1.9 respectively, p = 0.3), body (7.7 ± 1.9, 13 ± 9.2, 7.8 ± 1.9 respectively, p = 0.8), and duodenum (6.2 ± 2.1, 9.5 ± 6.8, 7.0 ± 1.8 respectively, p = 0.6). No correlation was observed between SUVmax uptake and either HbA1C or fasting blood glucose.Conclusions and InferencesFemale diabetic gastroparesis patients did not demonstrate increased TSPO ligand 11C‐ER 176 uptake in the stomach. Possible explanations include lack of specificity of ligand for specific macrophage phenotypes in DG, sex effect, or small sample size. Further studies investigating non‐invasive ways of analyzing immune dysregulation in neurogastrointestinal disorders are warranted.

AbstractBackgroundThe Rome IV irritable bowel syndrome (IBS) criteria include changes to the description and frequency of abdominal pain. Existing studies have demonstrated a lower prevalence and greater severity in IBS patients identified using Rome IV than Rome III criteria. Our aim was to investigate the prevalence of post‐infection IBS (PI‐IBS) using Rome IV criteria in a population‐based cohort of laboratory‐confirmed C. jejuni infection cases.MethodsThe Minnesota Department of Health (MDH) requires notification of Campylobacter cases and interviews patients to gather information on clinical symptoms. For this study, the Rome IV diagnostic questionnaire was utilized 6–9 months after infection to determine the development of PI‐IBS. The survey responses were analyzed for the prevalence of IBS and symptom severity.Key ResultsSurveys were completed by 391 participants (31% response rate). Twenty‐three patients had pre‐existing IBS, and 18 did not complete enough questions to categorize their case status. Of the 350 remaining participants, 58 (17%) met Rome IV criteria. An additional 47 patients would have met the Rome III IBS criteria for pain frequency, driving the cumulative prevalence to 30%. The mean IBS Symptom Severity Score (IBS‐SSS) in Rome IV patients was significantly higher than in Rome III (p < 0.05). With Rome IV, IBS‐diarrhea was the most common subtype.Conclusions & InferencesRome IV criteria resulted in a 19% lower prevalence of PI‐IBS than earlier reported Rome III‐based prevalence in a similar population. Rome IV defined PI‐IBS patients have greater symptom severity but similar distribution of IBS subtypes.

INTRODUCTION: Cannabidiol (CBD), a CBR2 agonist with limited psychic effects, antagonizes CB1/CB2 receptors. Allelic variation CNR1 (gene for CBR1) rs806378 and FAAH rs324420 were associated with altered gut motility and sensation. This study aimed to compare the pharmacodynamics and clinical effects of a 4-week treatment with pharmaceutical-grade CBD vs placebo and assess the interactions of FAAH and CNR1 gene variants on the effects of CBD in patients with functional dyspepsia (FD). METHODS: We performed a randomized, double-blinded, placebo-controlled (1:1 ratio) study of CBD b.i.d. (20 mg/kg/d according to the US Food and Drug Administration escalation guidance) in FD patients with nondelayed gastric emptying (GE) at baseline. Symptoms were assessed by validated daily symptom diary (0–4 scale for upper abdominal pain, nausea, and bloating), weekly assessment of adequate relief, Leuven Postprandial Distress Scale (8 symptoms, adjectival scores rated 0–4 for severity), and quality of life (Short-Form Nepean Dyspepsia Index [average of 10 dimensions each on a 5-point scale]). After the 4-week treatment, all patients underwent measurements of GE of solids, gastric volumes, and Ensure nutrient satiation test. Statistical analysis compared 2 treatments for all endpoints and the effects of CBD in association with FAAH rs324420 and CNR1 rs806378. RESULTS: CBD and placebo effects on physiological functions and patient response outcomes were not significantly different. There were borderline CBD treatment-by-genotype interactions: rs806378 CNR1 with Leuven Postprandial Distress Scale ( P = 0.06) and GE solids ( P = 0.12). DISCUSSION: Approved doses of CBD used off-label do not relieve FD with normal baseline GE of solids or alter gastric motor functions and satiation. CBD treatment-by-gene interactions suggest potential benefits for postprandial distress with CNR1 rs806378 T allele.

LINKED CONTENTThis article is linked to Grover et al and Elwing & Sayuk papers. To view these articles, visit https://doi.org/10.1111/apt.16591 and https://doi.org/10.1111/apt.16603

SummaryBackgroundIrritable bowel syndrome (IBS) patients often experience meal‐associated symptoms. However, the underlying mechanisms are unclear.AimTo determine small intestinal mechanisms of lipid‐induced symptoms and rectal hypersensitivity in IBSMethodsWe recruited 26 IBS patients (12 IBS‐C, 14 IBS‐D) and 15 healthy volunteers (HV). In vivo permeability was assessed using saccharide excretion assay. Rectal sensitivity was assessed using a barostat before and after small bowel lipid infusion; symptoms were assessed throughout. Next, an extended upper endoscopy with probe‐based confocal laser endomicroscopy (pCLE) was performed with changes induced by lipids. Duodenal and jejunal mucosal biopsies were obtained for transcriptomics.ResultsFollowing lipid infusion, a higher proportion of HV than IBS patients reported no pain, no nausea, no fullness and no urgency (P < 0.05 for all). In a model adjusted for sex and anxiety, IBS‐C and IBS‐D patients had lower thresholds for first rectal sensation (P = 0.0007) and pain (P = 0.004) than HV. In vivo small intestinal permeability and mean pCLE scores were similar between IBS patients and HV. Post‐lipid, pCLE scores were higher than pre‐lipid but were not different between groups. Baseline duodenal transient receptor potential vanilloid (TRPV) 1 and 3 expression was increased in IBS‐D, and TRPV3 in IBS‐C. Duodenal TRPV1 expression correlated with abdominal pain (r = 0.51, FDR = 0.01), and inversely with first rectal sensation (r = −0.48, FDR = 0.01) and pain (r = −0.41, FDR = 0.02) thresholds.ConclusionLipid infusion elicits a greater symptom response in IBS patients than HV, which is associated with small intestinal expression of TRPV channels. TRPV‐mediated small intestinal chemosensitivity may mediate post‐meal symptoms in IBS.

In vivo human studies evaluated concurrently the volume of the stomach during fasting and after a solid and liquid meal using a new SPECT-based method. Although fasting gastric volumes did not impact the rates of gastric emptying, both postprandial and accommodation volumes of the whole and proximal stomach were significantly correlated with gastric emptying. Larger stomach volumes were associated with slower gastric emptying.

INTRODUCTION: Intestinal pseudo-obstruction is characterized by impaired transit and luminal dilation in the absence of mechanical obstruction. Our study aims to describe the clinical, radiographic, and physiological findings in pseudo-obstruction associated with systemic sclerosis (SSc), amyloidosis, and paraneoplastic syndrome. METHODS: A retrospective cohort of patients evaluated at our institution between January 1, 2008, and August 1, 2018, was assembled. Clinical, imaging, and physiological characteristics were abstracted from electronic medical records. RESULTS: We identified 100 cases of pseudo-obstruction (55 SSc, 27 amyloidosis, and 18 paraneoplastic). Female population predominance was seen in SSc (71%) vs male population in amyloidosis (74%). Most common symptom was abdominal bloating in all 3 groups. Vomiting was more common in SSc than amyloidosis (73% vs 46%, P = 0.02). Diarrhea was more common in amyloidosis and SSc compared with paraneoplastic (81% and 67% vs 28%, P < 0.01). Weight loss (>5%) was more common in SSc compared with amyloidosis and paraneoplastic (78% vs 31% and 17%, P < 0.0001). Only small bowel dilation was seen in 79%, 40%, and 44% and only large bowel dilation in 2%, 44%, and 44% of patients in SSc, amyloidosis, and paraneoplastic, respectively. Five of 8 SSc patients had myopathic and 3 of 5 paraneoplastic had neuropathic involvement on gastroduodenal manometry. DISCUSSION: SSc-associated pseudo-obstruction demonstrates female population predominance and presents with vomiting, diarrhea, and weight loss. Amyloidosis-associated pseudo-obstruction shows male population predominance. Small bowel is more commonly involved than large bowel on both imaging and transit studies in SSc. Myopathic involvement was more common in SSc, contrary to neuropathic in paraneoplastic syndrome.