Berumen, Antonio

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.

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.

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.