Understanding the Role of Purinergic P2X7 Receptors in the Gastrointestinal System: A Systematic Review

Background: The role of purinergic P2X7 receptor (P2X7R) is of interest due to its involvement in inflammation and mediating immune cell responses. P2X7R is particularly implicated in the development of inflammatory bowel disease (IBD). However, the extent of the actions of P2X7R in the gastrointestinal (GI) system under physiological and pathophysiological conditions remains to be elucidated. This systematic review aimed to identify, summarize and evaluate the evidence for a critical role of P2X7R in the GI system.Methods: We searched PubMed, Embase and Scopus with search terms pertained to P2X7R in the GI system in disease or physiological state, including “P2X7 or P2X7 receptor or purinergic signaling” in combination with any of the terms “intestine or colon or gut or gastrointestinal,” “pathology or inflammation or disease or disorder,” and “physiology or expression.” Titles and abstracts were screened for potentially eligible full texts, and animal and human studies published in English were included in this study. Data were extracted from papers meeting inclusion criteria. Meta-analysis was not feasible given the study diversity.Results: There were 48 papers included in this review. We identified 14 experimental colitis models, three sepsis models and one ischemia-reperfusion injury model. Among them, 11 studies examined P2X7R in GI infections, six studies on immune cell regulation, four studies on GI inflammation, two studies on GI malignancies, three studies involving intestinal injury due to various causes, two studies on ATP-activated P2X7R in the GI system and two studies on metabolic regulation.Conclusion: Evidence supports P2X7R mediating inflammation and immune cell responses in GI inflammation, infections and injury due to IBD and other challenges to the intestinal wall. P2X7R inhibition by gene knockout or by application of P2X7R antagonists can reduce tissue damage by suppressing inflammation. P2X7R is also implicated in GI malignancies and glucose and lipid homeostasis. P2X7R blockade, however, did not always lead to beneficial outcomes in the various pathological models of study.

Targeting the Gut Mucosal Immune System Using Nanomaterials

The gastrointestinal (GI) tract is one the biggest mucosal surface in the body and one of the primary targets for the delivery of therapeutics, including immunotherapies. GI diseases, including, e.g., inflammatory bowel disease and intestinal infections such as cholera, pose a significant public health burden and are on the rise. Many of these diseases involve inflammatory processes that can be targeted by immune modulatory therapeutics. However, nonspecific targeting of inflammation systemically can lead to significant side effects. This can be avoided by locally targeting therapeutics to the GI tract and its mucosal immune system. In this review, we discuss nanomaterial-based strategies targeting the GI mucosal immune system, including gut-associated lymphoid tissues, tissue resident immune cells, as well as GI lymph nodes, to modulate GI inflammation and disease outcomes, as well as take advantage of some of the primary mechanisms of GI immunity such as oral tolerance.

No Associations Between Dairy Intake and Markers of Gastrointestinal Inflammation in Healthy Adult Cohort

Objectives We examined associations between reported dairy intake and markers of gastrointestinal (GI) inflammation in a healthy human adult population. We hypothesized there would be a negative association of yogurt intake with GI inflammation, suggesting a protective effect, and no associations of total dairy, fluid milk, and cheese intake with GI inflammation. Methods Participants completed up to 3 unannounced 24-hour dietary recalls using ASA24 and a Block 2014 Food Frequency Questionnaire (FFQ) to assess recent and habitual intake, respectively. Those who also provided a stool sample were included in this analysis (n = 342). Stool samples were stored on ice immediately after collection and homogenized within 24 hours. Inflammatory markers from stool, including calprotectin, neopterin, and myeloperoxidase were measured by ELISA along with LPS-binding protein (LBP) from plasma. Regression models tested associations between dairy intake variables and inflammatory markers with and without covariates: sex, age, and body mass index (BMI). As yogurt is episodically consumed, t-tests were used to examine differences in inflammatory marker levels between consumers (>1 cup per month reported in FFQ) and non-consumers. Each dairy variable was also expressed as a percentage of mean energy intake from 24-hour recalls and regressed with inflammatory markers. Results Without covariates, we found no associations between total dairy, fluid milk, and yogurt from both dietary assessments with any inflammatory markers. Cheese intake reported in the FFQ was positively associated with plasma LBP (P = 0.02). However, this association was not significant after covariate adjustment. There were no significant differences in GI inflammatory marker levels between yogurt consumers and non-consumers (P > 0.05). When expressed as a percentage of mean energy intake, cheese from ASA24 was associated with increased LBP (P = 0.03), but this was not significant after adjustment for covariates. There were no other associations of dairy variables as a percentage of energy intake with GI inflammatory markers. Conclusions We found no clinically relevant associations between dairy intake and markers of GI inflammation in a healthy human adult cohort. Funding Sources California Dairy Research Foundation, USDA ARS 2032–51,530-026–00D.

Faecal Inflammatory Biomarkers and Gastrointestinal Symptoms after Bariatric Surgery: A Longitudinal Study

<b><i>Background:</i></b> Bariatric surgery induces various gastrointestinal (GI) modifications. We performed the first study longitudinally assessing the effect of bariatric surgery on faecal inflammatory biomarker levels and its relation with GI complaints. <b><i>Method:</i></b> Faecal calprotectin, lactoferrin, and calgranulin-C levels were determined in 41 patients (34 Roux-en-Y [RYGB], 7 sleeves) before and at 6–16 weeks, 6 months, and 1 year after surgery. Changes in biomarker levels and percentage of patients above reference value were determined. Gastrointestinal symptom rating scale (GSRS) was used to assess GI complaints at corresponding time points. The postoperative relation between GSRS score and biomarker levels above reference value was investigated. <b><i>Results:</i></b> After RYGB, median calprotectin levels are significantly higher (&#x3e;188, 104–415 μg/g) than before surgery (40, 19–78 μg/g; <i>p</i> &#x3c; 0.001), and over 90% of patients have levels above reference value 1 year after surgery. Median lactoferrin was 0.4 (0.2–1.6) μg/g before, and &#x3e;5.9 (1.8–13.6) μg/g after surgery (<i>p</i> &#x3c; 0.001). Median calgranulin-C levels remained far below the reference value and were 0.13 (0.05–0.24) μg/g before and &#x3c;0.23 (0.06–0.33) μg/g after surgery. Similar results were found after sleeve gastrectomy. No difference was seen in GSRS score for patients with calprotectin and lactoferrin levels above reference values. <b><i>Conclusion:</i></b> Faecal inflammatory biomarkers calprotectin and lactoferrin, but not calgranulin-C, rise above reference values shortly after bariatric surgery and remain elevated in the majority of patients. The discrepancy between calprotectin and calgranulin-C levels suggests no GI inflammation. Furthermore, patients after RYGB with biomarkers above the population reference value do not seem to have more GI complaints.

PHAGE-2 Study: Supplemental Bacteriophages Extend Bifidobacterium animalis subsp. lactis BL04 Benefits on Gut Health and Microbiota in Healthy Adults

Probiotics are increasingly used by consumers and practitioners to reduce gastrointestinal (GI) distress and improve gut function. Here, we sought to determine whether the addition of supplemental bacteriophages (PreforPro) could enhance the effects of a common probiotic, Bifidobacterium animalis subsp. lactis (B. lactis) on GI health. A total of 68 participants were enrolled in a 4-week, randomized, parallel-arm, double-blind, placebo-controlled trial where primary outcomes included self-assessments of GI health, a daily stool log, and 16s rRNA analysis of gut microbial populations. We observed within-group improvements in GI inflammation (p = 0.01) and a trending improvement in colon pain (p = 0.08) in individuals consuming B. lactis with PreforPro, but not in the group consuming only the probiotic. There was also a larger increase in Lactobacillus and short-chain fatty acid-producing microbial taxa detected in the stool of participants taking PreforPro with B. lactis compared to the probiotic alone. Overall, these results suggest the addition of PreforPro as a combination therapy may alter gut ecology to extend the GI benefits of consuming B. lactis or other probiotics.

PHAGE-2 Study: Supplemental Bacteriophages Extend Bifidobacterium animals subsp. lactis BL04 Benefits on Gut Health and Microbiota

Probiotics are increasingly used by consumers and practitioners to reduce gastrointestinal (GI) distress and improve gut function. Here, we sought to determine whether addition of supplemental bacteriophages (PreforPro) could enhance the effects of a common probiotic, Bifidobacterium animalis subsp. lactis (B. lactis) on GI health. We conducted a 4-week, randomized, parallel-arm, double-blind, placebo-controlled trial where primary outcomes included self-assessments of GI health, a daily stool log, and 16s rRNA analysis of gut microbial populations. We observed within group improvements in GI inflammation (p=0.01) and a trending improvement in colon pain (p=0.08) in individuals consuming B. lactis with PreforPro, but not in the group consuming only the probiotic. There was also a larger increase in Lactobacillus and short chain fatty acid-producing microbial taxa detected in stool of participants taking PreforPro with B. lactis compared to the probiotic alone. Overall, these results suggest the addition of PreforPro as a combination therapy may alter gut ecology to extend the GI benefits of consuming B. lactis or other probiotics.

GI inflammation Increases Sodium-Glucose Cotransporter Sglt1

A correlation between gastrointestinal (GI) inflammation and gut hormones has reported that inflammatory stimuli including bacterial endotoxins, lipopolysaccharides (LPS), TNFα, IL-1β, and IL-6 induces high levels of incretin hormone leading to glucose dysregulation. Although incretin hormones are immediately secreted in response to environmental stimuli, such as nutrients, cytokines, and LPS, but studies of glucose-induced incretin secretion in an inflamed state are limited. We hypothesized that GI inflammatory conditions induce over-stimulated incretin secretion via an increase of glucose-sensing receptors. To confirm our hypothesis, we observed the alteration of glucose-induced incretin secretion and glucose-sensing receptors in a GI inflammatory mouse model, and we treated a conditioned media (Mϕ 30%) containing inflammatory cytokines in intestinal epithelium cells and enteroendocrine L-like NCI-H716 cells. In GI-inflamed mice, we observed that over-stimulated incretin secretion and insulin release in response to glucose and sodium glucose cotransporter (Sglt1) was increased. Incubation with Mϕ 30% increases Sglt1 and induces glucose-induced GLP-1 secretion with increasing intracellular calcium influx. Phloridzin, an sglt1 inhibitor, inhibits glucose-induced GLP-1 secretion, ERK activation, and calcium influx. These findings suggest that the abnormalities of incretin secretion leading to metabolic disturbances in GI inflammatory disease by an increase of Sglt1.

Vancomycin Relieves Mycophenolate Mofetil-Induced Gastrointestinal Toxicity by Eliminating Gut Bacterial β-Glucuronidase Activity

Mycophenolate mofetil (MMF) is commonly prescribed after transplantation and has proven advantages over other immunosuppressive drugs but gastrointestinal (GI) side effects frequently limit its use. The pathways involved in the metabolism of the prodrug MMF and the bioactive derivative mycophenolic acid (MPA) are well characterized but the mechanism responsible for toxicity is unknown. Here we extend our previous observation that an intact gut microbiome is required for MMF-induced toxicity and demonstrate that gut bacterial metabolism is responsible for the GI inflammation and weight loss associated with MMF exposure. In mice consuming MMF, the introduction of vancomycin alone was sufficient to prevent or reverse MMF-induced weight loss and colonic inflammation. MMF induced the expansion of bacteria expressing β-glucuronidase (GUS) in the cecum and proximal colon. GUS activity, which is responsible for the catabolism of glucuronidated MPA (MPAG) to free MPA, was increased in the presence of MMF and eliminated by vancomycin. Vancomycin eliminated multipleBacteroides spp. that flourished in the presence of MMF and prevented the breakdown of MPAG without negatively affecting serum MPA levels. Human data suggests that increased stool GUS activity can be associated with MMF-related toxicity. Our work provides a mechanism for the GI toxicity associated with MMF and a future direction for the development of therapeutics.

Mouse Gamma Herpesvirus MHV-68 Induces Severe Gastrointestinal (GI) Dilatation in Interferon Gamma Receptor-Deficient Mice (IFNγR−/−) That Is Blocked by Interleukin-10

Inflammatory bowel disease (IBD) and Clostridium difficile infection cause gastrointestinal (GI) distension and, in severe cases, toxic megacolon with risk of perforation and death. Herpesviruses have been linked to severe GI dilatation. MHV-68 is a model for human gamma herpesvirus infection inducing GI dilatation in interleukin-10 (IL-10)-deficient mice but is benign in wildtype mice. MHV-68 also causes lethal vasculitis and pulmonary hemorrhage in interferon gamma receptor-deficient (IFNγR−/−) mice, but GI dilatation has not been reported. In prior work the Myxomavirus-derived anti-inflammatory serpin, Serp-1, improved survival, reducing vasculitis and pulmonary hemorrhage in MHV-68-infected IFNγR−/− mice with significantly increased IL-10. IL-10 has been investigated as treatment for GI dilatation with variable efficacy. We report here that MHV-68 infection produces severe GI dilatation with inflammation and gut wall degradation in 28% of INFγR-/- mice. Macrophage invasion and smooth muscle degradation were accompanied by decreased concentrations of T helper (Th2), B, monocyte, and dendritic cells. Plasma and spleen IL-10 were significantly reduced in mice with GI dilatation, while interleukin-1 beta (IL-1β), IL-6, tumor necrosis factor alpha (TNFα) and INFγ increased. Treatment of gamma herpesvirus-infected mice with exogenous IL-10 prevents severe GI inflammation and dilatation, suggesting benefit for herpesvirus-induced dilatation.

The intestinal microbiota in the pathogenesis of inflammatory bowel diseases: new insights into complex disease

Inflammatory bowel diseases (IBD) are a group of chronic diseases of increasing worldwide prevalence characterized by gastrointestinal (GI) inflammation leading to debilitating symptoms and complications. The contribution of the intestinal microbiota to the pathogenesis and etiology of these diseases is an area of active research interest. Here, we discuss key mechanisms underlying the chronic inflammation seen in IBD as well as evidence implicating the intestinal microbiota in the development and potentiation of that inflammation. We also discuss recently published work in areas of interest within the field of microbial involvement in IBD pathogenesis – the importance of proper microecology within the GI tract, the evidence that the intestinal microbiota transduces environmental and genetic risk factors for IBD, and the mechanisms by which microbial products contribute to communication between microbe and host. There is an extensive body of published research on the evidence for microbial involvement in IBD; the goal of this review is to highlight the growing edges of the field where exciting and innovative research is pushing the boundaries of the conceptual framework of the role of the intestinal microbiota in IBD pathogenesis.