Blockade of the renin-angiotensin system prevents acute and immunologically relevant colitis in murine models

The role of gut-islet axis in pancreatic islet function and glucose homeostasis

The gastrointestinal tract plays a vital role in the occurrence and treatment of metabolic diseases. Recent studies have convincingly demonstrated a bidirectional axis of communication between the gut and islets, enabling the gut to influence glucose metabolism and energy homeostasis in animals strongly. The 'gut-islet axis' is an essential endocrine signal axis that regulates islet function through the dialogue between intestinal microecology and endocrine metabolism. The discovery of glucagon-like peptide-1 (GLP-1), gastric inhibitory peptide (GIP) and other gut hormones has initially set up a bridge between gut and islet cells. However, the influence of other factors remains largely unknown, such as the homeostasis of the gut microbiota and the integrity of the gut barrier. Although gut microbiota primarily resides and affect intestinal function, they also affect extra-intestinal organs by absorbing and transferring metabolites derived from microorganisms. As a result of this transfer, islets may be continuously exposed to gut-derived metabolites and components. Changes in the composition of gut microbiota can damage the intestinal barrier function to varying degrees, resulting in increased intestinal permeability to bacteria and their derivatives. All these changes contribute to the severe disturbance of critical metabolic pathways in peripheral tissues and organs. In this review, we have outlined the different gut-islet axis signalling mechanisms associated with metabolism and summarized the latest progress in the complex signalling molecules of the gut and gut microbiota. In addition, we will discuss the impact of the gut renin-angiotensin system (RAS) on the various components of the gut-islet axis that regulate energy and glucose homeostasis. This work also indicates that therapeutic approaches aiming to restore gut microbial homeostasis, such as probiotics and faecal microbiota transplantation (FMT), have shown great potential in improving treatment outcomes, enhancing patient prognosis and slowing down disease progression. Future research should further uncover the molecular links between the gut-islet axis and the gut microbiota and explore individualized microbial treatment strategies, which will provide an innovative perspective and approach for the diagnosis and treatment of metabolic diseases.

What do we know about the renin angiotensin system and inflammatory bowel disease?

INTRODUCTION

The renin-angiotensin system (RAS) is an important homeostatic pathway, with emerging evidence for the impact of its components on inflammation and fibrosis in gastrointestinal tissues. This review aims to review current knowledge of the physiological mechanism of RAS in inflammatory bowel disease (IBD), and potential therapeutic implications.

AREAS COVERED

An extensive online literature review including Pubmed, Medline, and Google Scholar was undertaken. Discussion on the components of the RAS, localization, and physiological functions in the gastrointestinal tract, preclinical, and clinical data in IBD, and the relation with SARS-Cov-2 are covered in this review.

EXPERT OPINION

RAS inhibition may have a role as anti-fibrotic adjunct therapy. Targeting the local gastrointestinal RAS with novel modes of delivery may be a target for future therapeutics for IBD, given the widespread availability and safety of current options as utilized in other diseases. Further insight into the mechanism and downstream effects of gastrointestinal ACE2 may lead to a better understanding of the pathogenesis of IBD.

Vitamin D Deficiency Exacerbates Colonic Inflammation Due to Activation of the Local Renin-Angiotensin System in the Colon

BACKGROUND

The renin-angiotensin system (RAS) is activated in inflammatory bowel disease (IBD), and vitamin D deficiency aggravates the development of colitis, but the relationship between the local colonic RAS and vitamin D is unclear with regard to the pathogenesis of IBD.

AIMS

To investigate whether vitamin D suppresses the local colonic RAS to prevent colonic mucosal inflammation in a mouse model of experimental colitis.

METHODS

C57BL/6 mice fed vitamin D-deficient (VDD) diet for 8 weeks were induced to colitis by 2,4,6-trinitrobenzenesulfonic acid (TNBS), with mice fed vitamin D-sufficient (VDS) diet as controls. Colitis severity was assessed by histology, and pro-inflammatory cytokines, RAS components, and signaling pathways were quantified by real-time RT-PCR and Western blotting.

RESULTS

C57BL/6 mice fed the VDD diet for 8 weeks exhibited significantly lower serum 25(OH)D₃ concentrations compared to mice fed the VDS diet. When these VDD mice were induced to colitis by TNBS, they exhibited more severe colonic inflammation and developed more severe colitis compared to the VDS counterparts. VDD diet feeding resulted in higher production of mucosal pro-inflammatory cytokines, higher activation of the myosin light chain kinase-tight junction regulatory pathway, and greater increases in mucosal permeability. VDD diet feeding also enhanced colonic RAS activation. Treatment with angiotensin II receptor blocker losartan markedly alleviated colitis in TNBS-induced VDD mice.

CONCLUSION

Vitamin D deficiency promotes colonic inflammation at least in part due to over activation of the local RAS in the colon.

Renin-angiotensin system in intestinal inflammation-Angiotensin inhibitors to treat inflammatory bowel diseases?

Inflammatory bowel diseases (IBDs) are chronic disorders of the gastrointestinal tract, which manifest in recurring gastrointestinal inflammation. The current treatment options of IBD are not curative and are lacking in aspects like prevention of fibrosis. New treatment options are needed to fulfil the unmet needs and provide alternatives to drugs with resistances and side effects. Drugs targeting the renin-angiotensin system (RAS), besides being antihypertensive, also possess anti-inflammatory and antifibrotic properties and could offer an inexpensive alternative to control inflammation and fibrosis in the gut. RAS inhibitors have been effective in preventing and alleviating colitis in preclinical studies, but available human data are still sparse. This review outlines the pathophysiological functions of RAS in the gut and summarizes preclinical studies utilizing pharmacological RAS inhibitors in the treatment of experimental colitis. We discuss the alterations in intestinal RAS and the available evidence of the benefits of RAS inhibitors for IBD patients. Retrospective studies comparing IBD patients using ACE inhibitors or angiotensin II receptor blockers have provided optimistic results regarding a milder disease course and fewer hospitalizations and corticosteroid use in patients using RAS inhibitors. Prospective studies are needed to evaluate the effectiveness of these promising medications in the treatment of IBD.

Renin-angiotensin system promotes colonic inflammation by inducing TH17 activation via JAK2/STAT pathway

Previous studies suggest that the renin-angiotensin system (RAS) is a pathogenic factor for colitis. The goal of this study was to elucidate the molecular mechanism whereby angiotensin II (ANG II) promotes colonic inflammation. We found that renin was highly induced in colonic biopsies from patients with ulcerative colitis or Crohn's disease, and colonic renin and ANG II levels were markedly increased in a 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis model, indicating that the colonic RAS is activated in colitis. Renin transgenic (RenTg) mice exhibited increased phosphorylation in Janus kinase-2 (JAK2) and signal transducer and activator of transcription1/3 (STAT1/3) within colonic mucosa at baseline and following TNBS induction, suggesting that ANG II promotes colonic inflammation via the JAK2/STAT1/3 pathway. Treatment with pan-JAK inhibitor tofacitinib blocked JAK2 and STAT1/3 phosphorylation, attenuated T helper (T_H)1 and T_H17 responses, alleviated colitis, and prevented death of RenTg mice in TNBS model. ANG II stimulated JAK2/STAT1/3 phosphorylation in both Jurkat T lymphocytes and HCT116 epithelial cells. In vitro polarization assays demonstrated that ANG II directly promoted T_H17 polarization, but not T_H1 polarization, via JAK2/STAT1/3. ANG II stimulation of transforming growth factor-β1 (TGFβ1), IL-6, myosin light chain kinase, and p53 upregulated modulator of apoptosis in HCT116 cells was also mediated by JAK2/STAT1/3. These observations suggest that ANG II promotes T_H17 polarization directly as well as indirectly by inducing production of T_H17-polarizing cytokines (e.g., TGFβ1 and IL-6) from colonic epithelial cells, both via the JAK2/STAT pathway. Therefore, colonic RAS promotes colonic inflammation, at least in part, by stimulating T_H17 activation. NEW & NOTEWORTHY This study demonstrates that the local renin-angiotensin system in the colon is activated in colitis development, which promotes mucosal T helper cell activation through the JAK2/STAT pathway. These observations provide molecular evidence that the renin-angiotensin system is a pathogenic factor for the development of inflammatory bowel diseases.