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

First evidence of epigenetic modulation of human gene methylation by microalga Aphanizomenon flos-aquae (AFA) in inflammation-related pathways in intestinal cells

The microalga Aphanizomenon flos-aquae (AFA) has garnered attention for its potential therapeutic benefits in various health conditions, primarily through its use in nutraceutical formulations. While biological effects of AFA have been extensively studied in preclinical models, including murine systems, its nutrigenomic and epigenetic impacts remain underexplored. This study investigates the potential epigenetic mechanisms of AFA, focusing on its ability to modulate DNA methylation, a key regulatory process in gene expression. Specifically, we examined the influence of AFA on the methylation status of genes encoding pro-inflammatory interleukins, as these cytokines play a crucial role in immune response modulation and inflammation. Given the known impact of AFA on inflammatory markers, we aimed to determine whether the effects of AFA involve direct or indirect modulation of DNA methylation patterns in genes associated with inflammation. Our findings, presented here for the first time, reveal the capacity of AFA to influence DNA methylation, with implications for its role in cellular regulatory processes. These results warrant further investigation into precise mechanisms of action of AFA and its potential in clinical applications targeting inflammation-related pathways.

Angiotensin-converting enzymes 1 and 2 in the feces: presence and catalytic activity in the rat 2,4,6-trinitrobenzene sulfonic acid-induced model of colitis

BACKGROUND AND AIM

Inflammatory bowel disease is challenging to diagnose. Fecal biomarkers offer noninvasive solutions. The renin-angiotensin-aldosterone system is implicated in intestinal inflammation. Angiotensin-converting enzyme (ACE) and angiotensin-converting enzyme 2 (ACE2) regulate its activity, but conflicting findings on these enzymes in colitis require further investigation. We aimed to assess ACE and ACE2 presence and activities in the feces, serum, and colon of 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced rats.

METHODS

Colitis was induced in male rats by rectal instillation of a 21% ethanolic TNBS solution. After rats' sacrifice, colonic portions, serum, and feces were collected. ACE and ACE2 presence in the feces was analyzed by western Blot, and colonic and serum enzymes' concentrations were quantified using ELISA kits. ACE activity was assessed using Hippuryl-His-Leu and Z-Phe-His-Leu as substrates. ACE2 activity was assessed using Mca-APK (Dnp) as a substrate in the presence and absence of DX600 (ACE2 inhibitor).

RESULTS

An ACE isoform of ~70 kDa was found only in the feces of TNBS-induced rats. ACE concentration was higher than that of ACE2 in the serum and the inflamed colon. ACE N-domain activity was higher than that of the C-domain in all matrices. ACE2 activity was higher in the feces of TNBS-induced animals compared to controls.

CONCLUSION

A 70 kDa ACE isoform only detected in the feces of TNBS-induced rats may have translational relevance. ACE N-domain seems to play a significant role in regulating colonic lesions. Further research using human samples is necessary to validate these findings.

Heterogeneity in protocols and outcomes to study the effect of renin-angiotensin system blockers in inflammatory bowel disease: A systematic review

BACKGROUND

The renin-angiotensin system (RAS) has been associated with inflammatory bowel disease (IBD), supporting translational relevance of RAS blockers. Comparability of study design/outcomes is fundamental for data analysis/discussion.

OBJECTIVES

We aimed at evaluating the heterogeneity among protocols and outcomes to study the effect of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers in IBD.

METHODS

This study was performed and reported in accordance with the Cochrane recommendations and PRISMA (PROSPERO-CRD42022323853). Systematic searches were performed in PubMed, Scopus and Web of Science. Studies that met the inclusion criteria were selected. Quality assessment of the studies was done with the SYRCLES's risk of bias tools for animal studies.

RESULTS

Thirty-five pre-clinical studies and six clinical studies were included. Chemical induction of colitis was the most used model, but variable doses of the induction agent were reported. All studies reported at least a disease activity index, a macroscopic score, or a histologic assessment, but these scores were methodologically heterogeneous and reported for different characteristics. Great heterogeneity was also found in drug interventions. Inflammatory markers assessed as outcomes were different across studies.

CONCLUSION

Lack of standardization of protocols and outcomes among studies threatens the evidence on how RAS blockers influence IBD outcomes.

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.

Inhibition of uterine contractility by guanine-based purines in non-pregnant rats

Growing evidence pointed out that guanine-based purines are able to modulate smooth muscle contractile activity of blood vessels and gastrointestinal tract. Since, so far, possible guanine-based purine modulation of uterine musculature is unknown, the aim of the present study was to investigate in vitro, using organ bath technique, guanosine and guanine effects on spontaneous uterine contraction, and uterine contraction induced by K⁺-depolarization and oxytocin in a non-pregnant rat. Guanosine, but not guanine, reduced the amplitude of spontaneous contraction of the uterine muscle in a dose-dependent manner. The inhibitory response was antagonized by S-(4-nitrobenzyl)-6-thioinosine (NBTI), a membrane nucleoside transporter inhibitor, but persisted in the presence of theophylline, a nonselective adenosine receptor antagonist, or propanolol, β₁/β₂ adrenoreceptor antagonist or blockers of a nitrergic pathway. In addition, potassium channel blockers did not influence guanosine-induced effects. Guanosine was able to inhibit the external calcium (Ca²⁺) influx-induced contraction, but it did not affect the contraction induced by high-KCl solution, indicating that guanosine does not interact with L-type voltage-gated calcium channel. Guanosine prevented/reduced uterine contractions induced by oxytocin, even in the absence of external calcium. In conclusion, guanosine is able to reduce both spontaneous and oxytocin-induced contractions of rat myometrium, likely subsequently to its intracellular intake. The blockade of extracellular Ca²⁺ influx and reduction of Ca²⁺ release from the intracellular store are the mechanisms involved in the guanosine-induced tocolytic effects.

Histomorphometry Changes and Decreased Reactivity to Angiotensin II in the Ileum and Colon of Streptozotocin-Induced Diabetic Rats

Diabetes mellitus (DM) is a chronic progressive metabolic disorder associated with several gastrointestinal complications, affecting up to 75% of patients. Knowing that Angiotensin II (AngII) also regulates intestinal contraction, we decided to evaluate changes in ileum and colon histomorphometry and AngII reactivity in a rat model of DM. Streptozotocin (STZ, 55 mg/kg) was administered to induce DM to 24 adult male Wistar rats. Diabetic rats displayed all the characteristic signs of type 1 DM (T1DM) and fecal excretion increased about 4-fold over 14 days, while the excretion of controls remained unaltered. Compared to controls, diabetic ileum and colon presented an increase in both macroscopic (length, perimeter and weight) and microscopic (muscular wall thickness) parameters. Functionally, AngII-induced smooth muscle contraction was lower in diabetic rats, except in the distal colon. These differences in the contractile response to AngII may result from an imbalance between AngII type 1 (antagonized by candesartan, 10 nM) and type 2 receptors activation (antagonized by PD123319, 100 nM). Taken together, these results indicate that an early and refined STZ-induced T1DM rat model already shows structural remodelling of the gut wall and decreased contractile response to AngII, findings that may help to explain diabetic dysmotility.

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.

Aging modifies receptor expression but not muscular contractile response to angiotensin II in rat jejunum

The involvement of renin-angiotensin system in the modulation of gut motility and age-related changes in mRNA expression of angiotensin (Ang II) receptors (ATR) are well accepted. We aimed to characterize, in vitro, the contractile responses induced by Ang II, in jejunum from young (3–6 weeks old) and old rats (≥ 1 year old), to evaluate possible functional differences associated to changes in receptor expression. Mechanical responses to Ang II were examined in vitro as changes in isometric tension. ATR expression was assessed by qRT-PCR. Ang II induced a contractile effect, antagonized by losartan, AT1R antagonist, and increased by PD123319, AT2R antagonist, as well by neural blocker ω-conotoxin and by nitric oxide (NO) synthase inhibitor. No difference in the response was observed between young and old groups. AT1 receptor-mediated contractile response was decreased by U-73122, phospholipase C (PLC) inhibitor; or 2-aminoethoxy-diphenylborate (2-APB), inositol triphosphate (IP₃) receptor inhibitor; or nifedipine, l-type calcium channel blocker. Age-related changes in the expression of both AT1 receptor subtypes, AT1a and AT1b, and of AT2 receptors were detected. In conclusion, Ang II modulates the spontaneous contractility of rat jejunum via postjunctional AT1 receptors, involving Ca²⁺ mobilization from intracellular stores, via PLC/IP₃ pathway, and Ca²⁺ influx from extracellular space, via l-type channels. Prejunctional AT2 receptors would counteract AT1 receptor effects, via NO synthesis. The observed age-related differences in the expression of all AT receptor subtypes are not reflected in the muscular contractile response to Ang II.

Interaction between Sars-CoV-2 structural proteins and host cellular receptors: From basic mechanisms to clinical perspectives

Severe acute respiratory syndrome coronavirus 2 (Sars-CoV-2) has caused a global pandemic that has affected the lives of billions of individuals. Sars-CoV-2 primarily infects human cells by binding of the viral spike protein to angiotensin-converting enzyme 2 (ACE2). In addition, novel means of viral entry are currently being investigated, including Neuropillin 1, toll-like receptors (TLRs), cluster of differentiation 147 (CD147), and integrin α5β1. Enriched expression of these proteins across metabolic regulatory organs/tissues, including the circulatory system, liver, pancreas, and intestine contributes to major clinical complications among COVID-19 patients, particularly the development of hypertension, myocardial injury, arrhythmia, acute coronary syndrome and increased coagulation in the circulatory system during and post-infection. Pre-existing metabolic disease, such as cardiovascular disease, obesity, diabetes, and non-alcoholic fatty liver disease, is associated with increased risk of hospitalization, persistent post-infection complications and worse outcomes in patients with COVID-19. This review overviews the biological features of Sars-CoV-2, highlights recent findings that delineate the pathological mechanisms of COVID-19 and the consequent clinical diseases.

Moderate Physical Exercise Activates ATR2 Receptors, Improving Inflammation and Oxidative Stress in the Duodenum of 2K1C Hypertensive Rats

Background: In addition to the cardiovascular and renal systems, the gastrointestinal tract also contains angiotensin ATR_1a, ATR_1b, and ATR₂. We previously observed that the 2Kidney-1Clip hypertension model elicits physical exercise and gastrointestinal dysmotility, which is prevented by renin-angiotensin system blockers. Here, we investigate the effect of physical exercise on inflammation, stress biomarkers, and angiotensin II receptors in the duodenum of 2K1C rats. Methods: Arterial hypertension was induced by the 2K1C surgical model. The rats were allocated in Sham, 2K1C, or 2K1C+Exercise groups. One week after surgery, they were submitted to a physical exercise protocol (running 5x/week, 60min/day). Next, we assessed their intestinal contractility, cytokine levels (TNF-α, IL-1β, and IL-6), oxidative stress levels (MPO, GSH, MDA, and SOD), and the gene expression of angiotensin receptors (ATR_1A, ATR_1B, and ATR₂). Results: In comparison with the Sham group, the 2K1C arterial hypertension decreased (p<0.05) the intestinal contractility. In comparison with 2K1C, the 2K1C+Exercise group exhibited lower (p<0.05) MPO activity (22.04±5.90 vs. 78.95±18.09 UMPO/mg tissue) and higher (p<0.05) GSH concentrations in intestinal tissues (67.63±7.85 vs. 31.85±5.90mg NPSH/mg tissue). The 2K1C+Exercise group showed lower (p<0.05) cytokine levels in the intestine than 2K1C rats. In comparison with the Sham group, the 2K1C+Exercise rats showed higher (p<0.05) gene expression of ATR₂ in the duodenum. Conclusion: 2K-1C hypertension elicits an oxidative stress and inflammation process in the duodenum. Physical exercise modulates the expression twice as much of ATR2 receptors, suggesting possible anti-inflammatory and antioxidant effects induced by exercise.

2,4,6-trinitrobenzenesulfonic acid-induced colitis in Rattus norgevicus: a categorization proposal

Reproducibility in animal research is crucial for its reliance and translational relevance. The 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced model of inflammatory bowel disease (IBD) is widely used but inconsistently and incompletely characterized throughout the literature. This hinders comparisons between studies and influences the low rate of translation of effective preclinical molecules. The purpose of this study was to categorize TNBS-induced colitis, based on macroscopic and microscopic scoring systems, and to identify basic routine parameters that could anticipate those categories. We retrospectively analysed male Wistar Rattus norvegicus (n=28 for the control group and n=87 for the TNBS group) and categorized TNBS-induced colitis in three phenotypes: Mild, Moderate and Severe colitis, as for human IBD. Also, we showed that the time course of food intake and fecal excretion (but not body weight, fluid intake or welfare scores) could foresee those categories. So, routine evaluation of food intake and fecal excretion may guide researchers in planning their experiments, selecting the animals with the severity of colitis that better matches their aims, or applying early humane endpoints to animals that will not be used in the experiments. In conclusion, categorizing TNBS-induced colitis enhances the reproducibility of data gathered with this experimental model and strengths its translational relevance.

Interaction between the Renin-Angiotensin System and Enteric Neurotransmission Contributes to Colonic Dysmotility in the TNBS-Induced Model of Colitis

Angiotensin II (Ang II) regulates colon contraction, acting not only directly on smooth muscle but also indirectly, interfering with myenteric neuromodulation mediated by the activation of AT₁ /AT₂ receptors. In this article, we aimed to explore which mediators and cells were involved in Ang II-mediated colonic contraction in the TNBS-induced rat model of colitis. The contractile responses to Ang II were evaluated in distinct regions of the colon of control animals or animals with colitis in the absence and presence of different antagonists/inhibitors. Endogenous levels of Ang II in the colon were assessed by ELISA and the number of AT₁/AT₂ receptors by qPCR. Ang II caused AT₁ receptor-mediated colonic contraction that was markedly decreased along the colons of TNBS-induced rats, consistent with reduced AT₁ mRNA expression. However, the effect mediated by Ang II is much more intricate, involving (in addition to smooth muscle cells and nerve terminals) ICC and EGC, which communicate by releasing ACh and NO in a complex mechanism that changes colitis, unveiling new therapeutic targets.

AphaMax®, an Aphanizomenon Flos-Aquae Aqueous Extract, Exerts Intestinal Protective Effects in Experimental Colitis in Rats

BACKGROUND

Aphanizomenon flos-aquae (AFA) is a unicellular cyanobacterium considered to be a "superfood" for its complete nutritional profile and beneficial properties. We investigated possible beneficial effects of an AFA extract, commercialized as AphaMax^®, containing concentrated amount of phycocyanins and phytochrome, in 2,4 dinitrobenzensulfonic acid(DNBS)-induced colitis in rats.

METHODS

Effects of preventive oral treatment of AphaMax^® (20, 50 or 100 mg/kg/day) in colitic rats were assessed and then macroscopic and microscopic analyses were performed to evaluate the inflammation degree. Myeloperoxidase (MPO) activity and NF-κB, pro-inflammatory citockines, cycloxygenase-2 (COX-2), and inducible NOS (iNOS) levels of expression were determined, as Reactive Oxygen Species (ROS) and nitrite levels.

RESULTS

AphaMax^® treatment attenuated the severity of colitis ameliorating clinical signs. AphaMax^® reduced the histological colonic damage and decreased MPO activity, NF-κB activation, as well as iNOS and COX-2 expression. AphaMax^® treatment improved the altered immune response associated with colonic inflammation reducing IL-1β, IL-6 expression. Lastly, AphaMax^® reduced oxidative stress, decreasing ROS and nitrite levels.

CONCLUSIONS

Preventive treatment with AphaMax^® attenuates the severity of the inflammation in DNBS colitis rats involving decrease of the NF-kB activation, reduction of iNOS and COX-2 expression, and inhibition of oxidative stress. Due its anti-inflammatory and antioxidant proprieties AphaMax^® could be a good candidate as a complementary drug in inflammatory bowel disease (IBD) treatment.

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.