Immunohistochemical localization of angiotensin II receptor and local renin-angiotensin system in human colonic mucosa

Systematic-Narrative Hybrid Literature Review: Crosstalk between Gastrointestinal Renin-Angiotensin and Dopaminergic Systems in the Regulation of Intestinal Permeability by Tight Junctions

In the first part of this article, the role of intestinal epithelial tight junctions (TJs), together with gastrointestinal dopaminergic and renin-angiotensin systems, are narratively reviewed to provide sufficient background. In the second part, the current experimental data on the interplay between gastrointestinal (GI) dopaminergic and renin-angiotensin systems in the regulation of intestinal epithelial permeability are reviewed in a systematic manner using the PRISMA methodology. Experimental data confirmed the copresence of DOPA decarboxylase (DDC) and angiotensin converting enzyme 2 (ACE2) in human and rodent enterocytes. The intestinal barrier structure and integrity can be altered by angiotensin (1-7) and dopamine (DA). Both renin-angiotensin and dopaminergic systems influence intestinal Na+/K+-ATPase activity, thus maintaining electrolyte and nutritional homeostasis. The colocalization of B0AT1 and ACE2 indicates the direct role of the renin-angiotensin system in amino acid absorption. Yet, more studies are needed to thoroughly define the structural and functional interaction between TJ-associated proteins and GI renin-angiotensin and dopaminergic systems.

The Effect of Renin-Angiotensin-Aldosterone System Blocking Agents on the Long-term Disease Course of Patients With Crohn's Disease

BACKGROUND

The renin-angiotensin-aldosterone system (RAAS) has been associated with gastrointestinal inflammation and fibrosis, suggesting that RAAS blockade may be beneficial in patients with inflammatory bowel disease. Using retrospective analysis, we aimed to compare the disease course of patients with Crohn's disease (CD) taking two commonly prescribed classes of RAAS-blocking agents.

STUDY

Patients with CD initiated on an angiotensin-converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB) between 2000 and 2016 were enrolled. Data on clinical, radiologic, and procedural surrogate markers of inflammatory bowel disease were collected in the subsequent 3, 5, and 10 years and compared with matched controls using univariate and multivariate analyses.

RESULTS

Compared with controls, patients taking ARBs had fewer instances of corticosteroid use (1.06 vs 2.88, P < 0.01) at 10 years. Patients taking ACEIs had an overall worse disease course, with more imaging studies (3.00 vs 1.75, P = 0.03) and endoscopic procedures (2.70 vs 1.78, P = 0.01) at 5 years, and more imaging studies (6.19 vs 3.50, P < 0.01), endoscopic procedures (5.91 vs 3.78, P < 0.01), and gastrointestinal operations (0.59 vs 0.18, P < 0.02) at 10 years. Results remained significant on multivariate analysis, adjusting for CD characteristics and the use of other antihypertensive medications.

CONCLUSIONS

Our study provides insight into the long-term use of RAAS-blocking agents in patients with CD, suggesting that differences exist among commonly prescribed medication classes. While ACEIs were associated with an overall worse disease course at 5 and 10 years, patients taking ARBs were noted to have fewer instances of corticosteroid use at 10 years. Future large-scale studies are needed to further explore this association.

Telmisartan loading thermosensitive hydrogel repairs gut epithelial barrier for alleviating inflammatory bowel disease

Inflammatory bowel disease (IBD) remains a global health concern with a complex and incompletely understood pathogenesis. In the course of IBD development, damage to intestinal epithelial cells and a reduction in the expression of tight junction (TJ) proteins compromise the integrity of the intestinal barrier, exacerbating inflammation. Notably, the renin-angiotensin system and angiotensin II receptor type 1 (AT1R) play a crucial role in regulating the pathological progression including vascular permeability, and immune microenvironment. Thus, Telmisartan (Tel), an AT1R inhibitor, loading thermosensitive hydrogel was constructed to investigate the potential of alleviating inflammatory bowel disease through rectal administration. The constructed hydrogel exhibits an advantageous property of rapid transformation from a solution to a gel state at 37°C, facilitating prolonged drug retention within the gut while mitigating irritation associated with rectal administration. Results indicate that Tel also exhibits a beneficial effect in ameliorating colon shortening, colon wall thickening, cup cell lacking, crypt disappearance, and inflammatory cell infiltration into the mucosa in colitis mice. Moreover, it significantly upregulates the expression of TJ proteins in colonic tissues thereby repairing the intestinal barrier damage and alleviating the ulcerative colitis (UC) disease process. In conclusion, Tel-loaded hydrogel demonstrates substantial promise as a potential treatment modality for IBD.

The renin-angiotensin-aldosterone system (RAAS) signaling pathways and cancer: foes versus allies

The renin-angiotensin-aldosterone system (RAAS), is an old system with new fundamental roles in cancer biology which influences cell growth, migration, death, and metastasis. RAAS signaling enhances cell proliferation in malignancy directly and indirectly by affecting tumor cells and modulating angiogenesis. Cancer development may be influenced by the balance between the ACE/Ang II/AT1R and the ACE2/Ang 1-7/Mas receptor pathways. The interactions between Ang II/AT1R and Ang I/AT2R as well as Ang1-7/Mas and alamandine/MrgD receptors in the RAAS pathway can significantly impact the development of cancer. Ang I/AT2R, Ang1-7/Mas, and alamandine/MrgD interactions can have anticancer effects while Ang II/AT1R interactions can be involved in the development of cancer. Evidence suggests that inhibitors of the RAAS, which are conventionally used to treat cardiovascular diseases, may be beneficial in cancer therapies.Herein, we aim to provide a thorough description of the elements of RAAS and their molecular play in cancer. Alongside this, the role of RAAS components in sex-dependent cancers as well as GI cancers will be discussed with the hope of enlightening new venues for adjuvant cancer treatment.

ACE and ACE2 catalytic activity in the fecal content along the gut

BACKGROUND

Angiotensin-converting enzyme (ACE) and ACE2 are two major enzymes of the renin-angiotensin-aldosterone system (RAAS), which control the formation/degradation of angiotensin (Ang) II and Ang1-7, regulating their opposite effects. We aimed at evaluating the catalytic activity of ACE and ACE2 in the intestinal content and corresponding intestinal tissue along the gut of Wistar Han rats.

METHODS

Portions of the ileum, cecum, proximal colon, and distal colon, and the corresponding intestinal content were collected from Wistar Han rats. Enzyme activity was evaluated by fluorometric assays using different substrates: Hippuryl-His-Leu for ACE-C-domain, Z-Phe-His-Leu for ACE-N-domain, and Mca-APK(Dnp) for ACE2. ACE and ACE2 concentration was assessed by ELISA. Ratios concerning concentrations and activities were calculated to evaluate the balance of the RAAS. Statistical analysis was performed using Friedman test followed by Dunn's multiple comparisons test or Wilcoxon matched-pairs test whenever needed.

KEY RESULTS

ACE and ACE2 are catalytically active in the intestinal content along the rat gut. The ACE N-domain shows higher activity than the C-domain both in the intestinal content and in the intestinal tissue. ACE and ACE2 are globally more active in the intestinal content than in the corresponding intestinal tissue. There was a distal-to-proximal prevalence of ACE2 over ACE in the intestinal tissue.

CONCLUSIONS & INFERENCES

This work is the first to report the presence of catalytically active ACE and ACE2 in the rat intestinal content, supporting future research on the regulatory role of the intestinal RAAS on gut function and a putative link to the microbiome.

Nutritional implications in the mechanistic link between the intestinal microbiome, renin-angiotensin system, and the development of obesity and metabolic syndrome

Obesity and metabolic disorders represent a significant global health problem and the gut microbiota plays an important role in modulating systemic homeostasis. Recent evidence shows that microbiota and its signaling pathways may affect the whole metabolism and the Renin-Angiotensin System (RAS), which in turn seems to modify microbiota. The present review aimed to investigate nutritional implications in the mechanistic link between the intestinal microbiome, renin-angiotensin system, and the development of obesity and metabolic syndrome components. A description of metabolic changes was obtained based on relevant scientific literature. The molecular and physiological mechanisms that impact the human microbiome were addressed, including the gut microbiota associated with obesity, diabetes, and hepatic steatosis. The RAS interaction signaling and modulation were analyzed. Strategies including the use of prebiotics, symbiotics, probiotics, and biotechnology may affect the gut microbiota and its impact on human health.

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.

The Angiotensin AT2 Receptor: From a Binding Site to a Novel Therapeutic Target

Discovered more than 30 years ago, the angiotensin AT2 receptor (AT2R) has evolved from a binding site with unknown function to a firmly established major effector within the protective arm of the renin-angiotensin system (RAS) and a target for new drugs in development. The AT2R represents an endogenous protective mechanism that can be manipulated in the majority of preclinical models to alleviate lung, renal, cardiovascular, metabolic, cutaneous, and neural diseases as well as cancer. This article is a comprehensive review summarizing our current knowledge of the AT2R, from its discovery to its position within the RAS and its overall functions. This is followed by an in-depth look at the characteristics of the AT2R, including its structure, intracellular signaling, homo- and heterodimerization, and expression. AT2R-selective ligands, from endogenous peptides to synthetic peptides and nonpeptide molecules that are used as research tools, are discussed. Finally, we summarize the known physiological roles of the AT2R and its abundant protective effects in multiple experimental disease models and expound on AT2R ligands that are undergoing development for clinical use. The present review highlights the controversial aspects and gaps in our knowledge of this receptor and illuminates future perspectives for AT2R research. SIGNIFICANCE STATEMENT: The angiotensin AT2 receptor (AT2R) is now regarded as a fully functional and important component of the renin-angiotensin system, with the potential of exerting protective actions in a variety of diseases. This review provides an in-depth view of the AT2R, which has progressed from being an enigma to becoming a therapeutic target.

ACEi/ARBs associate with lower incidence of gastrointestinal bleeding in peritoneal dialysis patients

BACKGROUND

Gastrointestinal bleeding (GIB) is widespread in patients with impaired renal function. Whether angiotensin-converting enzyme inhibitors/angiotensin II receptor blockers (ACEi/ARBs) potentially take a crucial role in avoiding GIB incidence among peritoneal dialysis (PD) patients is unknown.

METHODS

Overall, 734 PD patients were enrolled after using propensity score matching. Kaplan-Meier analysis and COX regression were used to explore correlation between ACEi/ARBs and GIB. Competitive risk model was aimed to identify whether other events were confounding factors. Forest plot was applied to assess the influence of ACEI/ARBs on GIB incidence in different groups.

RESULTS

During 8-year follow-up, 89 (12.13%) cases of GIB were recorded. Kaplan-Meier analysis revealed that the incidence of GIB among patients taking ACEi/ARBs was lower than those subjects who had not (log rank = 6.442, P = 0.011). After adjusted different confounding factors, administration of ACEi/ARBs was associated with lowered GIB incidence (adjusted HR = 0.49, 95% CI 0.32-0.77, P = 0.002). In competitive risk model, considering of other events, the incidence of GIB in two groups was still statistically significant (P = 0.010). Subgroup analysis showed ACEi/ARBs taking impeded GIB in the ≥ 60 age group (HR = 0.52, 95% CI 0.28-0.98, P = 0.040).

CONCLUSION

PD patients who were submitted to ACEi/ARBs inclined to have a lower risk for GIB. In this regard, ACEi/ARBs offered a promising choice to GIB.

Gut microbiota and renin-angiotensin system: a complex interplay at local and systemic levels

Gut microbiota is a potent biological modulator of many physiological and pathological states. The renin-angiotensin system (RAS), including the local gastrointestinal RAS (GI RAS), emerges as a potential mediator of microbiota-related effects. The RAS is involved in cardiovascular system homeostasis, water-electrolyte balance, intestinal absorption, glycemic control, inflammation, carcinogenesis, and aging-related processes. Ample evidence suggests a bidirectional interaction between the microbiome and RAS. On the one hand, gut bacteria and their metabolites may modulate GI and systemic RAS. On the other hand, changes in the intestinal habitat caused by alterations in RAS may shape microbiota metabolic activity and composition. Notably, the pharmacodynamic effects of the RAS-targeted therapies may be in part mediated by the intestinal RAS and changes in the microbiome. This review summarizes studies on gut microbiota and RAS physiology. Expanding the research on this topic may lay the foundation for new therapeutic paradigms in gastrointestinal diseases and multiple systemic disorders.

Development of Anti-fibrotic Therapy in Stricturing Crohn's Disease: Lessons from Randomized Trials in Other Fibrotic Diseases

Intestinal fibrosis is considered an inevitable complication of Crohn's disease (CD) that results in symptoms of obstruction and stricture formation. Endoscopic or surgical treatment is required to treat the majority of patients. Progress in the management of stricturing CD is hampered by the lack of effective anti-fibrotic therapy; however, this situation is likely to change because of recent advances in other fibrotic diseases of the lung, liver and skin. In this review, we summarized data from randomized controlled trials (RCT) of anti-fibrotic therapies in these conditions. Multiple compounds have been tested for the anti-fibrotic effects in other organs. According to their mechanisms, they were categorized into growth factor modulators, inflammation modulators, 5-hydroxy-3-methylgultaryl-coenzyme A (HMG-CoA) reductase inhibitors, intracellular enzymes and kinases, renin-angiotensin system (RAS) modulators and others. From our review of the results from the clinical trials and discussion of their implications in the gastrointestinal tract, we have identified several molecular candidates that could serve as potential therapies for intestinal fibrosis in CD.

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.

Receptor for advanced glycation end-products axis and coronavirus disease 2019 in inflammatory bowel diseases: A dangerous liaison?

Compelling evidence supports the crucial role of the receptor for advanced glycation end-products (RAGE) axis activation in many clinical entities. Since the beginning of the coronavirus disease 2019 pandemic, there is an increasing concern about the risk and handling of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in inflammatory gastrointestinal disorders, such as inflammatory bowel diseases (IBD). However, clinical data raised during pandemic suggests that IBD patients do not have an increased risk of contracting SARS-CoV-2 infection or develop a more severe course of infection. In the present review, we intend to highlight how two potentially important contributors to the inflammatory response to SARS-CoV-2 infection in IBD patients, the RAGE axis activation as well as the cross-talk with the renin-angiotensin system, are dampened by the high expression of soluble forms of both RAGE and the angiotensin-converting enzyme (ACE) 2. The soluble form of RAGE functions as a decoy for its ligands, and soluble ACE2 seems to be an additionally attenuating contributor to RAGE axis activation, particularly by avoiding the transactivation of the RAGE axis that can be produced by the virus-mediated imbalance of the ACE/angiotensin II/angiotensin II receptor type 1 pathway.

The Role of Angiotensin Converting Enzyme 2 in Modulating Gut Microbiota, Intestinal Inflammation, and Coronavirus Infection

The role of angiotensin converting enzyme 2 has expanded from regulating the renin angiotensin system to regulating intestinal amino acid homeostasis and the gut microbiome. Recently, angiotensin converting enzyme 2 was identified as a primary receptor for severe acute respiratory syndrome coronaviruses 1 and 2 being expressed in multiple tissues including the luminal surface of the gut. In this brief perspective, we examine the role of angiotensin converting enzyme 2 as the receptor for severe acute respiratory syndrome coronavirus 2 and the impact of coronavirus disease 19 infection on the gut microbiome and on the gut epithelium.

Elucidating the Association Between the Upregulation of Angiotensin Type 1-Receptors and the Development of Gastrointestinal Malignancies

The renin-angiotensin system (RAS) is a major regulator of body fluid hemostasis and blood pressure. Angiotensin type 1 receptors (AT1R) are one of the major components of this system and are widely expressed in different organs, including the gastrointestinal (GI) system. Very little known about the physiological roles of AT1R in GI tract but evidence has reported that local AT1Rs are upregulated in pathological conditions like GI malignancies and play role in stimulation of signaling pathways associated with GI cancers progression. AT1Rs axes signaling in tumor microenvironments stimulate inflammation and facilitate vascularization around the tumor cell to display invasive behavior. AT1Rs in stroma cells promote tumor-associated angiogenesis by upregulated of vessel endothelial growth factor (VEGF). Also, AT1Rs by the activation of molecular mechanisms such as PI3/Akt/NF-κB pathways increase the invasion of tumor cells. Experimental and clinical studies have reported that AT1R antagonists have beneficial influences by increasing the survival of patients with GI malignancies and reduction in the proliferation of GI cancer cell lines in vitro, and the growth and metastasis of tumors in vivo, therefore, AT1Rs antagonist have the potential for future anticancer strategies. This review focuses on the pathological roles of AT1Rs in GI malignancies.

Angiotensin II inhibits P-glycoprotein in intestinal epithelial cells

AIM

P-glycoprotein (Pgp/MDR1) plays a major role in intestinal homeostasis. Decrease in Pgp function and expression has been implicated in the pathogenesis of IBD. However, inhibitory mechanisms involved in the decrease of Pgp in inflammation are not fully understood. Angiotensin II (Ang II), a peptide hormone predominantly expressed in the epithelial cells of the crypt-villus junction of the intestine, has been shown to exert pro-inflammatory effects in the gut. It is increased in IBD patients and animals with experimental colitis. Whether Ang II directly influences Pgp is not known.

METHODS

Pgp activity was measured as verapamil-sensitive 3 H-digoxin flux. Pgp surface expression and exocytosis were measured by cell surface biotinylation studies. Signalling pathways were elucidated by Western blot analysis and pharmacological approaches.

RESULTS

Ang II (10 nM) significantly inhibited Pgp activity at 60 minutes. Ang II-mediated effects on Pgp function were receptor-mediated as the Ang II receptor 1 (ATR1) antagonist, losartan, blocked Pgp inhibition. Ang II effects on Pgp activity appeared to be mediated via PI3 kinase, p38 MAPK and Akt signalling. Ang II-mediated inhibition of Pgp activity was associated with a decrease in the surface membrane expression of Pgp protein via decreased exocytosis and was found to be dependent on the Akt pathway. Short-term treatment of Ang II (2 mg/kg b.wt., 2 hours) to mice also decreased the membrane expression of Pgp protein levels in ileum and colon.

CONCLUSION

Our findings provide novel insights into the role of Ang II and ATR1 in decreasing Pgp expression in intestinal inflammation.

The Therapeutic Potential of Angiotensin-converting Enzyme and Angiotensin Receptor Inhibitors in the Treatment of Colorectal Cancer: Rational Strategies and Recent Progress

Colorectal cancer (CRC) is one of the most common causes of cancer-related death in the world. There is a document that angiotensin (AT) which is found to be involved in the progression of CRC. Furthermore, Angiotensin receptor inhibitors (ARIs) and angiotensin-converting enzyme Inhibitors (ACE-Is) demonstrate activity in CRC by their inhibition of both Insulin-like growth factor 1 (IGF-1) and Vascular endothelial growth factor (VEGF), and therefore present a potentially novel therapeutic strategy in colorectal cancer, which have summarized in the current review. Preclinical studies have illustrated the direct effect of major active mediator angiotensin II (ATII) on the promotion of angiogenesis through VEGF and other proliferative mediators. Suppression of the angiotensin II type I receptor (AT1R) via ACE-Is has shown a reduction in the development of solid tumor and metastasis, particularly CRC incidence, polyp formation, and distant metastasis. MicroRNAs (miRs) are a family of small nucleotides without coding that plays an important role after transcribing hundreds to thousands of non-coding and coding gene. Against this background, the application of anti-hypertensive medications such as losartan might have a therapeutic impact, although further preclinical and clinical studies might provide novel insight into the potentially beneficial effect of ACE-Is in the treatment of colorectal cancer patients.

PD123319, angiotensin II type II receptor antagonist, inhibits oxidative stress and inflammation in 2, 4-dinitrobenzene sulfonic acid-induced colitis in rat and ameliorates colonic contractility

Angiotensin II, the main effector of renin angiotensin system, plays an important role in the inflammatory process and most of its effects are mediated through the AT1 receptor activation. However, the knowledge about the AT2 receptor involvement in this process is still evolving. We previously found that in an experimental model of colitis, AT2 receptor activation can contribute to the impairment of the muscle contractility in vitro in the course of inflammation. Here, we investigated the potential alleviating effects of the in vivo treatment of PD123319 (1-[[4-(Dimethylamino)-3-methylphenyl]methyl]-5-(diphenylacetyl)-4,5,6,7- tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid ditrifluoroacetate), AT2 receptor antagonist, in 2,4-dinitrobenzene sulfonic acid (DNBS)-induced rat model of colitis. The effects of i.p PD123319 (0.3, 3 and 10 mg/kg) administration to rats subjected to intra-rectal DNBS instillation were investigated. The study revealed that the colon injury and the inflammatory signs were ameliorated by PD123319 when visualized by the histopathological examination. The colon shortening, myeloperoxidase activity, and colonic expression of IL-1β, IL-6 and iNOS were downregulated in a dose-dependent manner in DNBS-induced colitis rats treated with PD123319 and the anti-oxidant defense machinery was also improved. The mechanism of these beneficial effects was found in the ability of PD123319 to inhibit NF-κB activation induced by DNBS. The colonic contractility in inflamed tissues was also improved by PD123319 treatment. In conclusion, our data have demonstrated previously that undescribed proinflammatory effects for the AT2 receptors in DNBS-induced colitis in rats in which they are mediated likely by NF-κB activation and reactive oxygen species generation. Moreover, when the inflammatory process is mitigated by the AT2 receptor antagonist treatment, the smooth muscle is able to recover its functionality.

Altered expression of renin-angiotensin system receptors throughout colorectal adenoma-adenocarcinoma sequence

Background and Objective: Colorectal cancer (CRC) is a major health problem in developed countries. Adenomatous lesions in the large bowel are the main precursors of CRC and the adenoma-adenocarcinoma sequence still provides a solid model for research on carcinogenesis. The finding of local renin-angiotensin systems (RAS) has been crucial to understand the role of this peptidergic system in cancer and has opened new perspectives in the study of colorectal carcinogenetic processes. Methods: In this study we analyzed the immunohistochemical expression of three main RAS receptors (AT1, AT2 and MAS) in a large series of CRC samples (n=161), including uninvolved intestinal mucosa-adenoma-adenocarcinoma sequences from the same patients (n=50). Results: 1) AT1 and AT2 showed a biphasic expression pattern along the sequence. The expression significantly decreased in adenomas with respect to uninvolved mucosa but increased in CRCs. 2) AT2 expression was lower in advanced CRCs with high local invasion (pT4), high stage (IV), high nodal (N2) and vascular invasion. 3) MAS receptor was moderately expressed in the uninvolved mucosa and in adenomas. This expression increased very significantly in CRC tissues. Conclusions: These results suggest that: 1) RAS receptors are differentially regulated as the genetic and epigenetic alterations accumulate throughout the uninvolved mucosa-adenoma-CRC sequence. 2) Loss of AT2 expression could contribute to the aggressive behavior of advanced CRC cells.

Losartan and Vitamin D Inhibit Colonic Tumor Development in a Conditional Apc-Deleted Mouse Model of Sporadic Colon Cancer

Colorectal cancer is a leading cause of cancer deaths. The renin-angiotensin system (RAS) is upregulated in colorectal cancer, and epidemiologic studies suggest RAS inhibitors reduce cancer risk. Because vitamin D (VD) receptor negatively regulates renin, we examined anticancer efficacy of VD and losartan (L), an angiotensin receptor blocker. Control Apc^+/LoxP mice and tumor-forming Apc^+/LoxP Cdx2P-Cre mice were randomized to unsupplemented Western diet (UN), or diets supplemented with VD, L, or VD+L, the latter to assess additive or synergistic effects. At 6 months, mice were killed. Plasma Ca²⁺, 25(OH)D3, 1α, 25(OH)2D3, renin, and angiotensin II (Ang II) were quantified. Colonic transcripts were assessed by qPCR and proteins by immunostaining and blotting. Cancer incidence and tumor burden were significantly lower in Cre+ VD and Cre+ L, but not in the Cre+ VD+L group. In Apc^+/LoxP mice, VD increased plasma 1,25(OH)2D3 and colonic VDR. In Apc^+/LoxP-Cdx2P-Cre mice, plasma renin and Ang II, and colonic tumor AT1, AT2, and Cyp27B1 were increased and VDR downregulated. L increased, whereas VD decreased plasma renin and Ang II in Cre+ mice. VD or L inhibited tumor development, while exerting differential effects on plasma VD metabolites and RAS components. We speculate that AT1 is critical for tumor development, whereas RAS suppression plays a key role in VD chemoprevention. When combined with L, VD no longer increases active VD and colonic VDR in Cre- mice nor suppresses renin and Ang II in Cre+ mice, likely contributing to lack of chemopreventive efficacy of the combination.

Renal tubular dysgenesis and microcolon, a novel association. Report of three cases

Renal tubular dysgenesis (RTD) is a developmental abnormality of the nephron characterized by fetal anuria, oligohydramnios, and severe postnatal hypotension. Genetic forms have an autosomal recessive inheritance and are caused by mutations in genes encoding key components of the renin-angiotensin pathway. We report three patients from two unrelated families with RTD due to pathogenic variants of the angiotensin-converting enzyme (ACE) gene, in whom RTD was associated with microcolon. We also detail key variations of the renin-angiotensin system in one of these infants. The severe intestinal developmental abnormality culminating in microcolon and early terminal ileum perforation/necrotizing enterocolitis is a novel finding not previously associated with RTD, which points to a role of the renin-angiotensin system in gut development.

Angtensin II elicits a cAMP-dependent intestinal anion secretion by stimulating PGE2 release through AT1 subtype receptors in rat ileum

A growing literature has demonstrated that the renin-angiotensin system (RAS) involves in gut function. Angiotensin II (AngII) stimulates Cl^- secretion in intestine epithelial cells. However, the underlying signal pathway remains unexplored. Here, we explored that serosal application of Ang II (5 × 10^-8 M) significantly increased the baseline Isc compared to the control group in rat ileum. Tetrodotoxin (TTX) failed to suppress Isc evoked by Ang II. However, the Ang II-evoked Isc was significantly suppressed by the ATR₁ antagonist losartan instead of ATR₂ antagonist PD123319. Of interest, both cyclooxygenase (COX)-1 inhibitor SC560 and COX-2 specific inhibitor ns398 blocked the Ang II-evoked Isc. Preincubation of submucosa/mucosa preparations with Ang II for 10 min significantly increased PGE2 production, which was abolished by either COX-1 or COX-2 inhibitor. In addition, the Ang II-induced PGE2 release was also attenuated by ATR₁ receptor antagonist rather than selective ATR₂ receptor antagonist. Furthermore, preincubation of tissues for 15 min with forskolin, a cAMP activator, markedly blocked the Isc evoked by AngII, while intracellular Ca²⁺ pump inhibitor thapsigargin, L-type Ca²⁺ channel blocker nicadipine or the epithelial Na⁺ channel blocker amiloride didn't show such function. These results suggest that Ang II evokes cAMP-activated intestinal anion secretion by stimulating PGE2 release through activation of ATR1.

Angiotensin II type II receptors and colonic dysmotility in 2,4-dinitrofluorobenzenesulfonic acid-induced colitis in rats

BACKGROUND

Angiotensin II (Ang II), the main peptide of the renin-angiotensin system (RAS), has been suggested to be involved in inflammatory bowel diseases. Since RAS has emerged as gut motility regulator, and dysmotility is associated with intestinal inflammation, our objective was to investigate in rat 2,4-dinitrobenzenesulfonic acid (DNBS)-induced colitis the functionality of RAS and its contribution to colonic motor alterations.

METHODS

The effects of Ang II on the longitudinal colonic muscular contractility of control and DNBS-treated rats were characterized in vitro. Transcripts encoding for Ang II receptors were investigated by RT-PCR.

KEY RESULTS

Inflamed preparations showed a longitudinal muscle marked hypocontractility. Angiotensin II caused contractile effects in both preparations, but the responses in DNBS preparations were reduced compared to controls. In both preparations, Losartan, AT₁ receptor antagonist, reduced Ang II effects. PD123319, AT₂ receptor antagonist, enhanced Ang II responses only in DNBS rats, as well as N^ω -Nitro-L-arginine (L-NNA), nitric oxide (NO) synthase inhibitor, or tetrodotoxin (TTX), neural toxin. The co-administration of PD123319 and TTX or L-NNA produced no additive effects. PD123319 per se improved colonic contractility in inflamed tissues. The effect was reduced in the presence of L-NNA or TTX. All Ang II receptor subtypes were expressed in both preparations.

CONCLUSIONS & INFERENCES

AT₁ receptors mediate Ang II contractile responses in rat colon. During inflammation a recruitment of Ang II AT₂ receptors would counteract AT₁ -contractile activity. A tonic activation of AT₂ receptors would contribute to the general reduction in muscle contractility during experimental inflammation. A role for enteric neurons and NO is also suggested.

Effects of Antihypertensive Agents on Intestinal Contractility in the Spontaneously Hypertensive Rat: Angiotensin Receptor System Downregulation by Losartan

Hypertension is an inflammatory condition controlled by the renin angiotensin system and is linked to kidney disease, diabetes mellitus, and recently to dysfunction of the gut. The aim of this study was to determine what effect antihypertensive drug treatments may have on intestinal function of the spontaneously hypertensive rat (SHR). In the first experiment, SHRs were treated with enalapril, hydralazine, or with no treatment as a control. In the second experiment, SHRs were treated with losartan or with no treatment as a control. All drug treatments led to significant lowering of blood pressure after 16 weeks. At termination, intact tissue sections of the ileum and colon were induced to contract ex vivo by KCl; electrical stimulation; and agonists carbachol, angiotensin II, and prostaglandin E₂ (PGE₂). There were no differences in ileal or colonic contractility due to hydralazine or enalapril compared with no-treatment SHR control. However, for the ileum, the losartan group responded significantly more to KCl and carbachol while responding less to angiotensin II, with no difference for PGE₂ compared with the no-treatment SHR control. In contrast, the colon responded similarly to KCl, electrical stimulation, and PGE₂ but responded significantly less to angiotensin II. These results demonstrate that the ileum responds differently (with KCl and carbachol as agonists) to the colon after losartan treatment, whereas there is a reduced contractile response in both the ileum and colon following losartan treatment. Although there are few well documented major contraindications for angiotensin receptor blockers, the modulation of gut contractility by losartan may have wider implications for bowel health.

Angiotensin II Type 1 Receptor-Dependent GLP-1 and PYY Secretion in Mice and Humans

Angiotensin II (Ang II) is the key hormone mediator of the renin angiotensin system, which regulates blood pressure and fluid and electrolyte balance in the body. Here we report that in the colonic epithelium, the Ang II type 1 receptor is highly and exclusively expressed in enteroendocrine L cells, which produce the gut hormones glucagon-like peptide-1 and peptide YY (PYY). Ang II stimulated glucagon-like peptide-1 and PYY release from primary cultures of mouse and human colon, which was antagonized by the specific Ang II type 1 receptor blocker candesartan. Ang II raised intracellular calcium levels in L cells in primary cultures, recorded by live-cell imaging of L cells specifically expressing the fluorescent calcium sensor GCaMP3. In Ussing chamber recordings, Ang II reduced short circuit currents in mouse distal colon preparations, which was antagonized by candesartan or a specific neuropeptide Y1 receptor inhibitor but insensitive to amiloride. We conclude that Ang II stimulates PYY secretion, in turn inhibiting epithelial anion fluxes, thereby reducing net fluid secretion into the colonic lumen. Our findings highlight an important role of colonic L cells in whole-body fluid homeostasis by controlling water loss through the intestine.

The renin-angiotensin system in Barrett's esophagus

OBJECTIVE

Barrett's esophagus (BE) is a risk factor for esophageal adenocarcinoma. In addition to its classical endocrine character known for hemodynamic regulation, the renin-angiotensin system (RAS) can be associated with inflammation, wound healing, and cancer. The aim of this study was to explore a potential expression of the RAS in BE, with or without the presence of dysplasia.

MATERIAL AND METHODS

Biopsy material was prepared for western blotting and immunohistochemistry. Non-BE patients (controls) were compared with BE patients regarding RAS in the squamous epithelium. In the columnar BE mucosa, RAS expression was studied in patients with and without dysplasia. Key components of the 'classical' RAS were assessed: the angiotensin-converting enzyme (ACE) and the angiotensin II subtype 1 and 2 receptors (AT1R and AT2R).

RESULTS

The presence of RAS factors was confirmed in the esophageal mucosa of both control and BE patients. ACE protein expression was 48% lower (p = 0.001) whereas AT1R was 45% higher (p = 0.039) in the squamous epithelium of BE patients compared to epithelia from non-BE controls. In the metaplastic intestinal-like epithelium, AT1R expression was 37% higher in BE patients with confirmed dysplasia than in patients without dysplasia (p = 0.009). Immunohistochemistry showed an altered distribution of RAS proteins in BE patients with dysplasia.

CONCLUSIONS

The differential RAS expression observed may prove to be useful as a biomarker or a pharmaceutical target.

Dietary peptides from the non-digestible fraction of Phaseolus vulgaris L. decrease angiotensin II-dependent proliferation in HCT116 human colorectal cancer cells through the blockade of the renin–angiotensin system

Peptides in common beans reduced angiotensin II-dependent proliferation in HCT116 colon cancer cells.

Pathogenic aspects and therapeutic avenues of intestinal fibrosis in Crohn's disease

In Crohn's disease, one of the two major forms of inflammatory bowel diseases in human beings, persistent and chronic inflammation promotes fibrotic processes thereby facilitating formation of strictures, the most common indication for surgical intervention in this disorder. The pathogenesis of Crohn's disease-associated fibrosis is not fully understood, but variants of genes involved in the recognition of microbial components/products [e.g. CARD15 (caspase-activating recruitment domain 15) and ATG16L1 (autophagy-related 16-like 1)] are associated with this phenotype, and experimental evidence suggests that intestinal fibrosis results from an altered balance between deposition of ECM (extracellular matrix) and degradation of ECM by proteases. Studies have also contributed to identify the main phenotypic and functional alterations of cells involved in the fibrogenic process, as well as molecules that stimulate such cells to produce elevated amounts of collagen and other ECM-related proteins. In the present review, we assess the current knowledge about cellular and molecular mediators of intestinal fibrosis and describe results of recent studies aimed at testing the preventive/therapeutic effect of compounds in experimental models of intestinal fibrosis.

AT1R blocker losartan attenuates intestinal epithelial cell apoptosis in a mouse model of Crohn's disease

Angiotensin II, which is the main effector of the renin-angiotensin system, has an important role in intestinal inflammation via the angiotensin II type 1 receptor (AT1R). The present study aimed to investigate the protective effects of the AT1R blocker losartan on 2,4,6-trinitrobenzenesulphonic acid (TNBS)-induced colitis. Losartan was administered to male adult C57BL/6 J mice 2 weeks prior to the induction of colitis, and images of the whole colon were captured to record changes, scored according to a microscopic scoring system, and reverse transcription-quantitative polymerase chain reaction were performed in order to investigate colonic inflammation. In addition, intestinal epithelial barrier permeability was evaluated, and intestinal epithelial cell (IEC) apoptosis was measured using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining, and apoptosis-related protein expression levels were detected by western blotting. Losartan was able to attenuate TNBS-induced body weight loss and colonic damage. Furthermore, T helper 1-mediated proin-flammatory cytokines were suppressed by losartan, and gut permeability was largely preserved. TUNEL staining revealed reduced IEC apoptosis in the losartan-treated mice. Losartan also increased the B-cell lymphoma 2 (Bcl-2)/Bcl-2-associated X protein (Bax) ratio and suppressed caspase-3 induction. These results suggested that the AT1R blocker losartan may attenuate TNBS-induced colitis by inhibiting the apoptosis of IECs. The effects of losartan were partially mediated through increasing the Bcl-2/Bax ratio and subsequently suppressing the induction of the proapoptotic mediator caspase-3.

Opposing tissue-specific roles of angiotensin in the pathogenesis of obesity, and implications for obesity-related hypertension

Metabolic disease, specifically obesity, has now become the greatest challenge to improving cardiovascular health. The renin-angiotensin system (RAS) exists as both a circulating hormone system and as a local paracrine signaling mechanism within various tissues including the brain, kidney, and adipose, and this system is strongly implicated in cardiovascular health and disease. Growing evidence also implicates the RAS in the control of energy balance, supporting the concept that the RAS may be mechanistically involved in the pathogenesis of obesity and obesity hypertension. Here, we review the involvement of the RAS in the entire spectrum of whole organism energy balance mechanisms, including behaviors (food ingestion and spontaneous physical activity) and biological processes (digestive efficiency and both aerobic and nonaerobic resting metabolic rates). We hypothesize that opposing, tissue-specific effects of the RAS to modulate these various components of energy balance can explain the apparently paradoxical results reported by energy-balance studies that involve stimulating, versus disrupting, the RAS. We propose a model in which such opposing and tissue-specific effects of the RAS can explain the failure of simple, global RAS blockade to result in weight loss in humans, and hypothesize that obesity-mediated uncoupling of endogenous metabolic rate control mechanisms can explain the phenomenon of obesity-related hypertension.

Activation of angiotensin II type 1 receptors and contractile activity in human sigmoid colon in vitro

AIM

To analyse the effects of angiotensin II (Ang II) on the contractility of human sigmoid colon, and to characterize the subtype(s) of receptor(s) involved and the related action mechanism.

METHODS

The contractility of sigmoid colon circular muscle strips was recorded isometrically. RT-PCR and immunohistochemistry were used to reveal the eventual existence of a local renin-angiotensin system (RAS) and the distribution of Ang II receptors.

RESULTS

Transcripts encoding for the Ang II type 1 (AT1 ) and the Ang II type 2 (AT2 ) receptor subtypes and for the angiotensin-converting enzyme in the whole-thickness muscular wall were observed. Ang II caused a concentration-dependent contractile response, which is antagonized by losartan, AT1 receptor antagonist, but not by PD123319, AT2 receptor antagonist. The joint application of losartan and PD123319 did not produce any additive effect. The contractile response to Ang II was partially reduced by tetrodotoxin, Na(+) voltage-gated neural channel blocker, and to some extent by SR48968, tachykinin NK2 receptor antagonist. However, hexamethonium, nicotinic receptor antagonist, atropine, cholinergic muscarinic receptor antagonist and SR140333, tachykinin NK1 receptor antagonist, were ineffective. Immunohistochemical analysis showed that AT1 receptors were expressed on the smooth muscle layers and myenteric plexus.

CONCLUSION

Ang II positively modulates the spontaneous contractile activity of human sigmoid colon via activation of post-junctional and pre-junctional AT1 receptors, the latter located on the enteric nerves that modulate the release of tachykinins. The presence of the components of RAS in the human colon suggests that Ang II can be also locally generated to control colonic motility.

Dietary Sodium Suppresses Digestive Efficiency via the Renin-Angiotensin System

Dietary fats and sodium are both palatable and are hypothesized to synergistically contribute to ingestive behavior and thereby obesity. Contrary to this hypothesis, C57BL/6J mice fed a 45% high fat diet exhibited weight gain that was inhibited by increased dietary sodium content. This suppressive effect of dietary sodium upon weight gain was mediated specifically through a reduction in digestive efficiency, with no effects on food intake behavior, physical activity, or resting metabolism. Replacement of circulating angiotensin II levels reversed the effects of high dietary sodium to suppress digestive efficiency. While the AT₁ receptor antagonist losartan had no effect in mice fed low sodium, the AT₂ receptor antagonist PD-123,319 suppressed digestive efficiency. Correspondingly, genetic deletion of the AT₂ receptor in FVB/NCrl mice resulted in suppressed digestive efficiency even on a standard chow diet. Together these data underscore the importance of digestive efficiency in the pathogenesis of obesity, and implicate dietary sodium, the renin-angiotensin system, and the AT₂ receptor in the control of digestive efficiency regardless of mouse strain or macronutrient composition of the diet. These findings highlight the need for greater understanding of nutrient absorption control physiology, and prompt more uniform assessment of digestive efficiency in animal studies of energy balance.

Interactions of the renin-angiotensin system in colorectal cancer and metastasis

The novel function of the renin-angiotensin system (RAS) is cardiovascular homeostasis. While the major active mediator angiotensin II (ANG II) produces most of the physiologic responses via angiotensin II type I receptor (AT1R), recent insights have looked at the implications of ANG II and its impact on solid tumor formation. Preclinical studies have demonstrated the direct effect of ANG II on the stimulation of angiogenesis via VEGF and other proliferative mediators. RAS components have thus been identified in numerous malignant tissues. Inhibition of the AT1R via angiotensin-converting enzyme inhibitors (ACE-Is) has demonstrated a decrease in solid tumor development and metastasis. Numerous retrospective analyses have demonstrated a reduction in colorectal cancer incidence, polyp formation, and distant metastasis in patients taking inhibitors of the RAS. The use of commonly prescribed anti-hypertensive medications as a chemo-preventative medication may have a remarkable impact in the colorectal cancer community. Further investigation and prospective clinical trials may provide further insight into the potentially beneficial use of ACE-Is and their impact on colorectal cancer.

Central role of IL-17/Th17 immune responses and the gut microbiota in the pathogenesis of intestinal fibrosis

PURPOSE OF REVIEW

Intestinal fibrosis is a serious, yet common, outcome in patients with inflammatory bowel disease (IBD). Despite advances in developing novel treatment modalities to control chronic gut inflammation characteristic of IBD, no effective antifibrotic therapies exist to date. As such, a deeper understanding of the molecular mechanisms underlying intestinal fibrosis and the availability of relevant animal models are critical to move this area of investigation forward.

RECENT FINDINGS

Emerging concepts in the pathogenesis of intestinal fibrosis include the central role of interleukin (IL)-17 and Th17 immune responses, although their precise contribution to chronic inflammation and IBD remains controversial. Other novel mediators of intestinal fibrosis, such as tumor necrosis factor-like ligand 1A and components of the renin-angiotensin system, support the importance of IL-17. Additionally, recent studies utilizing novel mouse models highlight the significance of the gut microbiota and link components of bacterial sensing, including nucleotide-binding oligomerization domain-containing protein 2, to IL-17/Th17 immune responses in the development of inflammation-associated intestinal fibrosis.

SUMMARY

Recent progress in identifying key mediators, novel animal models, and important mechanistic pathways in the pathogenesis of intestinal fibrosis holds promise for the development of effective antifibrotics in an area of significant, unmet clinical need.

The renin-angiotensin system mediates EGF receptor-vitamin d receptor cross-talk in colitis-associated colon cancer

PURPOSE

We previously showed that EGF receptor (EGFR) promotes tumorigenesis in the azoxymethane/dextran sulfate sodium (AOM/DSS) model, whereas vitamin D suppresses tumorigenesis. EGFR-vitamin D receptor (VDR) interactions, however, are incompletely understood. Vitamin D inhibits the renin-angiotensin system (RAS), whereas RAS can activate EGFR. We aimed to elucidate EGFR-VDR cross-talk in colorectal carcinogenesis.

EXPERIMENTAL DESIGN

To examine VDR-RAS interactions, we treated Vdr(+/+) and Vdr(-/-) mice with AOM/DSS. Effects of VDR on RAS and EGFR were examined by Western blotting, immunostaining, and real-time PCR. We also examined the effect of vitamin D3 on colonic RAS in Vdr(+/+) mice. EGFR regulation of VDR was examined in hypomorphic Egfr(Waved2) (Wa2) and Egfr(wild-type) mice. Angiotensin II (Ang II)-induced EGFR activation was studied in cell culture.

RESULTS

Vdr deletion significantly increased tumorigenesis, activated EGFR and β-catenin signaling, and increased colonic RAS components, including renin and angiotensin II. Dietary VD3 supplementation suppressed colonic renin. Renin was increased in human colon cancers. In studies in vitro, Ang II activated EGFR and stimulated colon cancer cell proliferation by an EGFR-mediated mechanism. Ang II also activated macrophages and colonic fibroblasts. Compared with tumors from Egfr(Waved2) mice, tumors from Egfr(wild-type) mice showed upregulated Snail1, a suppressor of VDR, and downregulated VDR.

CONCLUSIONS

VDR suppresses the colonic RAS cascade, limits EGFR signals, and inhibits colitis-associated tumorigenesis, whereas EGFR increases Snail1 and downregulates VDR in colonic tumors. Taken together, these results uncover a RAS-dependent mechanism mediating EGFR and VDR cross-talk in colon cancer.

Medical therapy of stricturing Crohn's disease: what the gut can learn from other organs - a systematic review

Crohn’s disease (CD) is a chronic remitting and relapsing disease. Fibrostenosing complications such as intestinal strictures, stenosis and ultimately obstruction are some of its most common long-term complications. Despite recent advances in the pathophysiological understanding of CD and a significant improvement of anti-inflammatory therapeutics, medical therapy for stricturing CD is still inadequate. No specific anti-fibrotic therapy exists and the incidence rate of strictures has essentially remained unchanged. Therefore, the current therapy of established fibrotic strictures comprises mainly endoscopic dilation as well as surgical approaches. However, these treatment options are associated with major complications as well as high recurrence rates. Thus, a specific anti-fibrotic therapy for CD is urgently needed. Importantly, there is now a growing body of evidence for prevention as well as effective medical treatment of fibrotic diseases of other organs such as the skin, lung, kidney and liver. In face of the similarity of molecular mechanisms of fibrogenesis across these organs, translation of therapeutic approaches from other fibrotic diseases to the intestine appears to be a promising treatment strategy. In particular transforming growth factor beta (TGF-β) neutralization, selective tyrosine kinase inhibitors, blockade of components of the renin-angiotensin system, IL-13 inhibitors and mammalian target of rapamycin (mTOR) inhibitors have emerged as potential drug candidates for anti-fibrotic therapy and may retard progression or even reverse established intestinal fibrosis. However, major challenges have to be overcome in the translation of novel anti-fibrotics into intestinal fibrosis therapy, such as the development of appropriate biomarkers that predict the development and accurately monitor therapeutic responses. Future clinical studies are a prerequisite to evaluate the optimal timing for anti-fibrotic treatment approaches, to elucidate the best routes of application, and to evaluate the potential of drug candidates to reach the ultimate goal: the prevention or reversal of established fibrosis and strictures in CD patients.

Upregulation of circulating components of the alternative renin-angiotensin system in inflammatory bowel disease: A pilot study

INTRODUCTION

The relationship between intestinal inflammation and circulating components of the renin-angiotensin system (RAS) is poorly understood.

MATERIALS AND METHODS

Demographic and clinical data were obtained from healthy controls and patients with inflammatory bowel disease (IBD). Plasma concentrations of the classical RAS components (angiotensin-converting enzyme (ACE) and angiotensin II (Ang II)) and alternative RAS components (ACE2 and angiotensin (1-7) (Ang (1-7))) were analysed by radioimmuno- and enzymatic assays. Systemic inflammation was assessed using serum C-reactive protein (CRP), white cell count, platelet count and albumin, and intestinal inflammation by faecal calprotectin.

RESULTS

Nineteen healthy controls (11 female; mean age 38 years, range 23-68), 19 patients with Crohn's disease (11 female; aged 45 years, range 23-76) and 15 patients with ulcerative colitis (6 female; aged 42 years, 26-64) were studied. Circulating classical RAS component levels were similar across the three groups, whereas ACE2 activity and Ang (1-7) concentrations were higher in patients with IBD compared to controls (ACE2: 21.5 vs 13.3 pmol/ml/min, p<0.05; Ang (1-7): 22.8 vs 14.1 pg/ml, p<0.001). Ang (1-7) correlated weakly with platelet and white cell counts, but not calprotectin or CRP, in patients with IBD.

CONCLUSIONS

Circulating components of the alternative RAS are increased in patients with IBD.

Enalapril inhibits nuclear factor-κB signaling in intestinal epithelial cells and peritoneal macrophages and attenuates experimental colitis in mice

AIMS

Enalapril, an angiotensin-converting enzyme (ACE) inhibitor, has pleiotropic effects such as anti-inflammatory effects. This study investigated the effect of enalapril on the nuclear factor-kappa B (NF-κB) pathway and on experimental colitis.

MAIN METHODS

The human intestinal epithelial cell (IEC) line COLO 205 and peritoneal macrophages from C57BL/6 wild-type mice and IL-10-deficient (IL-10(-/-)) mice were prepared and subsequently stimulated with lipopolysaccharide (LPS) alone or LPS plus enalapril. The effect of enalapril on NF-κB signaling was examined by western blotting to detect IκBα phosphorylation/degradation; an electrophoretic mobility shift assay (EMSA) to assess the DNA binding activity of NF-κB; and ELISAs to qualify IL-8, TNF-α, IL-6, and IL-12 production. In in vivo studies, dextran sulfate sodium (DSS)-induced acute colitis in wild-type mice and chronic colitis in IL-10(-/-) mice were treated with or without enalapril. Colitis was quantified by histologic scoring, and the phosphorylation of IκBα in the colonic mucosa was assessed using immunohistochemistry.

KEY FINDINGS

Enalapril significantly inhibited LPS-induced IκBα phosphorylation/degradation, NF-κB binding activity, and pro-inflammatory cytokine production in both IEC and peritoneal macrophages. The administration of enalapril significantly reduced the severity of colitis, as assessed based on histology in both murine colitis models. Furthermore, in colon tissue, the up-regulation of IκBα phosphorylation with colitis induction was attenuated in enalapril-treated mice.

SIGNIFICANCE

Enalapril may block the NF-κB signaling pathway, inhibit the activation of IECs and macrophages, and attenuate experimental murine colitis by down-regulating IκBα phosphorylation. These findings suggest that enalapril is a potential therapeutic agent for inflammatory bowel disease.

Role of angiotensin-(1-7) in gastroprotection against stress-induced ulcerogenesis. The involvement of mas receptor, nitric oxide, prostaglandins, and sensory neuropeptides

Angiotensin-(1-7) [Ang-(1-7)] is a major vasoactive metabolite of angiotensin I (Ang I), both being important components of the renin-angiotensin system (RAS). Ang-(1-7) acting via Mas receptor was documented in kidneys, heart, brain, and gastrointestinal (GI)-tract. We studied the gastroprotective activity of exogenous Ang-(1-7) in rats exposed to water immersion and restraint stress (WRS) without or with A-779 [d-Ala7-Ang-(1-7), an antagonist of Ang-(1-7) Mas receptors], AVE 0991 (5-formyl-4-methoxy-2-phenyl-1[[4-[2-(ethylaminocarbonylsulfonamido)-5-isobutyl-3-thienyl]-phenyl]-methyl]-imidazole), the agonist of Ang-(1-7) receptor, as well as the inhibition of nitric-oxide (NO) synthase, the suppression of cyclo-oxygenase (COX)-1 (indomethacin, SC-560 [5-(4-chloro-phenyl)-1-(4-methoxyphenyl)-3-trifluoromethyl-pyrazole]), the activity COX-2 (rofecoxib), and denervation with capsaicin. The mRNA expression of constitutively expressed nitric-oxide synthase (cNOS), inducible nitric-oxide synthase (iNOS), interleukin (IL)-1β, and tumor necrosis factor (TNF)-α was analyzed by reverse transcription polymerase chain reaction. The WRS lesions were dose-dependently reduced by pretreatment with Ang-(1-7), which also caused an increase in gastric blood flow (GBF) and luminal content of NO. COX-1 and COX-2 inhibitors or L-NNA (N5-[imino(nitroamino)methyl]-L-ornithine) reversed the reduction in lesion number and the rise in GBF evoked by Ang-(1-7). Ang II augmented the WRS lesions, decreased GBF and increased the plasma IL-1β and TNF-α levels. Capsaicin denervation attenuated the reduction of Ang-(1-7)-induced gastric lesions and the rise in GBF; these effects were restored by supplementation with calcitonin gene-related peptide (CGRP). The cNOS mRNA was upregulated while iNOS, IL-1β and TNF-α mRNAs were downregulated in Ang-(1-7)-pretreated rats. We conclude that Ang-(1-7), in contrast to Ang II, which worsened WRS ulcerogenesis, affords potent gastroprotection against WRS ulcerogenesis via an increase in GBF mediated by NO, endogenous prostaglandins, sensory neuropeptides, and anti-inflammatory action involving the inhibition of proinflammatory markers iNOS, IL-1β, and TNF-α.

The renin-angiotensin system in the esophageal mucosa of healthy subjects and patients with reflux disease

OBJECTIVE

Components of the renin-angiotensin system (RAS) were recently discovered in the esophagus, which could be of interest in relation to gastroesophageal reflux disease (GERD). The present study was undertaken to confirm and further investigate the expression of RAS in healthy and refluxed exposed human esophageal mucosae.

METHODS

Esophageal biopsies were obtained from healthy subjects (n = 34) and individuals with erosive reflux disease (ERD, n = 28). Evaluation of general morphology and histological signs of reflux as well as investigation of gene transcript, protein expression and localization of various RAS components using RT-PCR, ELISA, western blot and immunohistochemistry were performed. Physiological effects of the AT2R were investigated in Ussing chamber experiments.

RESULTS

The study confirmed histological signs of reflux in ERD and expression of ACE, AT1R, AT2R and CatD in all examined specimens. In addition, the main effector peptide AngII, the pro-hormone AGT, the Mas receptor and the angiotensin-forming enzymes renin, CMA, CatG and NEP were present. Individuals with reflux disease had higher transcription activity of ACE and AT1R, increased protein levels of AT2R and lower levels of MasR. AT2R stimulation increased the ion currents in healthy epithelium, whereas epithelium from individuals with reflux disease exhibited no significant response.

CONCLUSIONS

The study demonstrated that a local RAS is present in the human esophageal epithelium. Some RAS components were significantly altered in individuals diagnosed with ERD suggesting involvement in the pathophysiology of GERD.

Cellular and molecular mechanisms of intestinal fibrosis

Fibrosis is a chronic and progressive process characterized by an excessive accumulation of extracellular matrix (ECM) leading to stiffening and/or scarring of the involved tissue. Intestinal fibrosis may develop in several different enteropathies, including inflammatory bowel disease. It develops through complex cell, extracellular matrix, cytokine and growth factor interactions. Distinct cell types are involved in intestinal fibrosis, such as resident mesenchymal cells (fibroblasts, myofibroblasts and smooth muscle cells) but also ECM-producing cells derived from epithelial and endothelial cells (through a process termed epithelial- and endothelial-mesenchymal transition), stellate cells, pericytes, local or bone marrow-derived stem cells. The most important soluble factors that regulate the activation of these cells include cytokines, chemokines, growth factors, components of the renin-angiotensin system, angiogenic factors, peroxisome proliferator-activated receptors, mammalian target of rapamycin, and products of oxidative stress. It soon becomes clear that although inflammation is responsible for triggering the onset of the fibrotic process, it only plays a minor role in the progression of this condition, as fibrosis may advance in a self-perpetuating fashion. Definition of the cellular and molecular mechanisms involved in intestinal fibrosis may provide the key to developing new therapeutic approaches.

Losartan reduces trinitrobenzene sulphonic acid-induced colorectal fibrosis in rats

BACKGROUND

Intestinal fibrosis is a challenging clinical condition in several fibrostenosing enteropathies, particularly Crohn's disease. Currently, no effective preventive measures or medical therapies are available for intestinal fibrosis. Fibrosis, due to an abnormal accumulation of extracellular matrix proteins, is a chronic and progressive process mediated by cell⁄matrix⁄cytokine and growth factor interactions, but may be a reversible phenomenon. Of the several molecules regulating fibrogenesis, transforming growth factor-beta 1 (TGF-b1) appears to play a pivotal role; it is strongly induced by the local activation of angiotensin II. The levels of both TGF-b1 and angiotensin II are elevated in fibrostenosing Crohn's disease.

AIMS

To evaluate the in vivo effect of losartan - an angiotensin II receptor antagonist - on the course of chronic colitis-associated fibrosis and on TGF-b1 expression.

METHODS

Colitis was induced by intrarectal instillation of trinitrobenzene sulphonic acid (TNBS) (15 mg⁄mL) while losartan was administered orally daily by gavage (7 mg⁄kg⁄day) for 21 days. Three groups of rats were evaluated: control (n=10); TNBS treated (n=10); and TNBS + losartan treated (n=10). Inflammation and fibrosis of the colon were evaluated by macro- and microscopic score analysis. Colonic TGF-b1 levels was measured using ELISA.

RESULTS

Twenty-one days after induction, losartan significantly improved the macro- and microscopic scores of fibrosis in the colonic wall and reduced TGF-b1 concentration.

CONCLUSIONS

Prophylactic oral administration of losartan reduces the colorectal fibrosis complicating the TNBS-induced chronic colitis, an effect that appears to be mediated by a downregulation of TGF-b1 expression.

Review article: the pathophysiological roles of the renin-angiotensin system in the gastrointestinal tract

BACKGROUND

The renin-angiotensin system (RAS) is a homeostatic pathway widely known to regulate cardiovascular and renal physiology; however, little is known about its influence in gastrointestinal tissues.

AIM

To elicit the anatomical distribution and physiological significance of the components of the RAS in the gastrointestinal tract.

METHODS

An extensive online literature review including Pubmed and Medline.

RESULTS

There is evidence for RAS involvement in gastrointestinal physiology and pathophysiology, with all the components required for autonomous regulation identified throughout the gastrointestinal tract. The RAS is implicated in the regulation of glucose, amino acid, fluid and electrolyte absorption and secretion, motility, inflammation, blood flow and possibly malignant disease within the gastrointestinal tract. Animal studies investigating the effects of RAS blockade in a range of conditions including inflammatory bowel disease, functional gut disorders, gastrointestinal malignancy and even intestinal ischaemia have been encouraging to date. Given the ready availability of drugs that modify the RAS and their excellent safety profile, an opportunity exists for investigation of their possible therapeutic role in a variety of human gastrointestinal diseases.

CONCLUSIONS

The gastrointestinal renin-angiotensin system appears to be intricately involved in a number of physiological processes, and provides a possible target for novel investigative and therapeutic approaches.

Use of enterally delivered angiotensin II type Ia receptor antagonists to reduce the severity of colitis

BACKGROUND

Renin-angiotensin system blockade reduces inflammation in several organ systems. Having found a fourfold increase in angiotensin II type Ia receptor expression in a dextran sodium sulfate colitis model, we targeted blockade with angiotensin II type Ia receptor antagonists to prevent colitis development. Because hypotension is a major complication of angiotensin II type Ia receptor antagonists use, we hypothesized that use of angiotensin II type Ia receptor antagonists compounds which lack cell membrane permeability, and thus enteric absorption, would allow for direct enteral delivery at far higher concentrations than would be tolerated systemically, yet retain efficacy.

METHODS

Based on the structure of the angiotensin II type Ia receptor antagonist losartan, deschloro-losartan was synthesized, which has extremely poor cell membrane permeability. Angiotensin II type Ia receptor antagonist efficacy was evaluated by determining the ability to block NF-κB activation in vitro. Dextran sodium sulfate colitis was induced in mice and angiotensin II type Ia receptor antagonist efficacy delivered transanally was assessed.

RESULTS

In vitro, deschloro-losartan demonstrated near equal angiotensin II type Ia receptor blockade compared to losartan as well as another angiotensin II type Ia receptor antagonist, candesartan. In the dextran sodium sulfate model, each compound significantly improved clinical and histologic scores and epithelial cell apoptosis. Abundance of TNF-α, IL-1β, and IL6 mRNA were significantly decreased with each compound. In vitro and in vivo intestinal drug absorption, as well as measures of blood pressure and mucosal and colonic blood flow, showed significantly lower uptake of deschloro-losartan compared to losartan and candesartan.

CONCLUSIONS

This study demonstrated efficacy of high-dose angiotensin II type Ia receptor antagonists in this colitis model. We postulate that a specially designed angiotensin II type Ia receptor antagonist with poor oral absorption may have great potential as a new therapeutic agent for inflammatory bowel disease in the future.

The renin-angiotensin system and the gastrointestinal mucosa

The gastrointestinal (GI) tract is fundamental for the intake of fluid and electrolytes and accommodates a large proportion of bodily hemodynamics and host defence systems. Despite that the renin-angiotensin system (RAS) is a prominent regulatory system for fluid and electrolyte homeostasis its impact on GI physiology is only little explored. Recent data indicate that RAS is well expressed and active in the GI tract although exact physiological roles are to be settled. There are several reports showing influences by RAS and its key mediator angiotensin II (AngII) on intestinal epithelial fluid and electrolyte transport and data are accumulating, suggesting involvement in GI mucosal inflammation and carcinogenesis. Of particular interest is the increasing amount of experimental support for the involvement of AngII formation and actions via the AngII subtype 1 (AT1) receptor in the pathogenesis and treatment of inflammatory bowel disease. The picture of RAS in the GI tract is, however, far from complete. Because RAS is an important application area for reno-cardiovascular diseases, a number of pharmacological agents as well as research technologies already exist and can in the future be used for GI research. A marked expansion of knowledge concerning the role of RAS in GI physiology and pathophysiology is to be expected.

Differential expression of angiotensin II type 1 and type 2 receptors at the maternal–fetal interface: potential roles in early placental development

Angiotensin II (Ang II) is locally generated in the placenta and regulates syncytial transport, vascular contractility and trophoblast invasion. It acts through two receptor subtypes, AGTR1 and AGTR2 (AT1 and AT2), which typically mediate antagonising actions. The objectives of this study are to characterise the cellular distribution of AGTR1 and AGTR2 at the maternal–fetal interface and explore the effects on cytotrophoblast turnover. Low levels ofAGTR2mRNA were detected in first trimester placental homogenates using real-time PCR. Immunohistochemistry using polyclonal antibodies against AGTR1 and AGTR2 detected the receptors in first trimester placenta, decidua basalis and villous tip outgrowths in culture. Serial staining with cytokeratin-7 was used to identify extravillous trophoblasts (EVTs). AGTR1 was found in the syncytiotrophoblast microvillous membrane, in a subpopulation of villous cytotrophoblasts, and in Hofbauer cells. AGTR1 was strongly upregulated in cytotrophoblasts in cell columns and villous tip outgrowths, but was absent in interstitial and endovascular EVTs within the decidua. AGTR2 immunostaining was present in Hofbauer cells and villous cytotrophoblasts, but was absent from syncytiotrophoblast. Faint staining was detected in cell column cytotrophoblasts and villous outgrowths, but not in EVTs within the decidua. Both receptors were detected in placental homogenates by western blotting. Ang II significantly increased proliferation of cytotrophoblasts in both villous explants and villous tip outgrowths, but did not affect apoptosis. Blockade of AGTR1 and AGTR2 together abrogated this effect. This study shows specific expression patterns for AGTR1 and AGTR2 in distinct trophoblast populations at the maternal–fetal interface and suggests that Ang II plays a role in placental development and generation of EVTs.

miR-802 regulates human angiotensin II type 1 receptor expression in intestinal epithelial C2BBe1 cells

Studies have demonstrated that angiotensin II (Ang II) can regulate intestinal fluid and electrolyte transport and control intestinal wall muscular activity. Ang II is also a proinflammatory mediator that participates in inflammatory responses such as apoptosis, angiogenesis, and vascular remodeling; accumulating evidence suggests that this hormone may be involved in gastrointestinal (GI) inflammation and carcinogenesis. Ang II binds to two distinct G protein-coupled receptor subtypes, the AT(1)R and AT(2)R, which are widely expressed in the GI system. Together these studies suggest that Ang II-AT(1)R/-AT(2)R actions may play an important role in GI tract physiology and pathophysiology. Currently it is not known whether miRNAs can regulate the expression of the human AT(1)R (hAT(1)R) in the GI system. PCR and in situ hybridization experiments demonstrated that miR-802 was abundantly expressed in human colon and intestine. Luciferase reporter assays demonstrated that miR-802 could directly interact with the bioinformatics-predicted target site harbored within the 3'-untranslated region of the hAT(1)R mRNA. To validate that the levels of miR-802 were physiologically relevant in the GI system, we demonstrated that miR-802 "loss-of-function" experiments resulted in augmented hAT(1)R levels and enhanced Ang II-induced signaling in a human intestinal epithelial cell line. These results suggest that miR-802 can modulate the expression of the hAT(1)R in the GI tract and ultimately play a role in regulating the biological efficacy of Ang II in this system.

Blockage of angiotensin II type 1 receptor regulates TNF-alpha-induced MAdCAM-1 expression via inhibition of NF-kappaB translocation to the nucleus and ameliorates colitis

Mucosal vascular addressin cell adhesion molecule 1 (MAdCAM-1) is an important target in the treatment of inflammatory bowel disease (IBD). Recently, treatment of IBD with an antibody to alpha4beta7-integrin, a ligand for MAdCAM-1, has been an intense focus of research. Our aim was to clarify the mechanism by which MAdCAM-1 is regulated via angiotensin II type 1 receptor (AT1R), and to verify if AT1R might be a novel target for IBD treatment. The role of AT1R in the expression of MAdCAM-1 in SVEC (a murine high endothelial venule cell) and MJC-1 (a mouse colonic endothelial cell) was examined following cytokine stimulation. We further evaluated the effect of AT1R on the pathogenesis of immune-mediated colitis using AT1R-deficient (AT1R-/-) mice and a selective AT1R blocker. AT1R blocker significantly suppressed MAdCAM-1 expression induced by TNF-alpha, but did not inhibit phosphorylation of p38 MAPK or of IkappaB that modulate MAdCAM-1 expression. However, NF-kappaB translocation into the nucleus was inhibited by these treatments. In a murine colitis model induced by dextran sulfate sodium, the degree of colitis, judged by body weight loss, histological damage, and the disease activity index, was much milder in AT1R-/- than in wild-type mice. The expression of MAdCAM-1 was also significantly lower in AT1R-/- than in wild-type mice. These results suggest that AT1R regulates the expression of MAdCAM-1 under colonic inflammatory conditions through regulation of the translocation of NF-kappaB into the nucleus. Furthermore, inhibition of AT1R ameliorates colitis in a mouse colitis model. Therefore, AT1R might be one of new therapeutic target of IBD via regulation of MAdCAM-1.

Angiotensin II receptor expression and relation to Helicobacter pylori-infection in the stomach of the Mongolian gerbil

Background

The role of the renin-angiotensin system in gastric physiology and disease has as yet been sparsely explored. The first aim of the study was to investigate the baseline presence and location of angiotensin II receptors (AT1R and AT2R) in the stomach of the Mongolian gerbil. A second aim was to elucidate whether the presence of H. pylori infection is associated with changes in the expression of these receptors.

Methods

H. pylori-negative and H. pylori-infected (strain SS1 or TN2GF4) male Mongolian gerbils were investigated. The stomachs were examined at six or 12 months after inoculation by the use of immunohistochemistry, western blot and microscopic morphometry.

Results

AT1R and AT2R were located in a variety of cells in the gerbil gastric wall, including a subpopulation of endocrine cells in the antral mucosa and inflammatory cells infiltrating H. pylori-infected stomachs. Gerbils infected with the SS1 strain showed a significantly increased antral AT1R protein expression and an increased number of infiltrating polymorphonuclear leucocytes (PMNs) at 12 months. The AT1R protein expression correlated with the number of PMNs and the antral expression of myeloperoxidase.

Conclusions

Angiotensin II receptors are present in a variety of cells in the gastric wall of the Mongolian gerbil. The results indicate an influence dependent on the H. pylori strain on the gastric AT1R expression and a relationship between gastric AT1R expression and mucosal PMNs infiltration.

Angiotensin II receptors are expressed and functional in human esophageal mucosa

Only few studies have been devoted to the actions of the renin-angiotensin system (RAS) in the human gastrointestinal tract. The present study was undertaken to elucidate the expression and action of RAS in the human esophageal mucosa. Mucosal specimens with normal histological appearance were obtained from healthy subjects undergoing endoscopy and from patients undergoing esophagectomy due to neoplasm. Gene and protein expressions of angiotensin II (Ang II) receptor type 1 (AT(1)) and type 2 (AT(2)) and angiotensin-converting enzyme (ACE) were analyzed. In vivo functionality in healthy volunteers was reflected by assessing transmucosal potential difference (PD). Ussing chamber technique was used to analyze the different effects of Ang II on its AT(1) and AT(2) receptors. Immunoreactivity to AT(1) and AT(2) was localized to stratum superficiale and spinosum in the epithelium. ACE, AT(1), and AT(2) were found in blood vessel walls. Transmucosal PD in vivo increased following administration of the AT(1) receptor antagonist candesartan. In Ussing preparations mean basal transmural PD was -6.4 mV, epithelial current (I(ep)) 34 muA/cm(2), and epithelial resistance (R(ep)) 321 Omega.cm(2). Serosal exposure to Ang II increased PD as a result of increased I(ep), whereas R(ep) was constant. Ang II given together with the selective AT(1)-receptor antagonist losartan, or AT(2) agonist C21 given alone, resulted in a similar effect. Ang II given in presence of the AT(2)-receptor antagonist PD123319 did not influence PD, but I(ep) decreased and R(ep) increased. In conclusion, Ang II receptors and ACE are expressed in the human esophageal epithelium. The results suggest that AT(2)-receptor stimulation increases epithelial ion transport, whereas the AT(1) receptor inhibits ion transport and increases R(ep).