Unraveling the Role of ACE2, the Binding Receptor for SARS-CoV-2, in Inflammatory Bowel Disease

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.

The Evaluation of Drugs as Potential Modulators of the Trafficking and Maturation of ACE2, the SARS-CoV-2 Receptor

ACE2, part of the angiotensin-converting enzyme family and the renin-angiotensin-aldosterone system (RAAS), plays vital roles in cardiovascular and renal functions. It is also the primary receptor for SARS-CoV-2, enabling its entry into cells. This project aimed to study ACE2's cellular trafficking and maturation to the cell surface and assess the impact of various drugs and compounds on these processes. We used cellular and biochemical analyses to evaluate these compounds as potential leads for COVID-19 therapeutics. Our screening assay focused on ACE2 maturation levels and subcellular localization with and without drug treatments. Results showed that ACE2 maturation is generally fast and robust, with certain drugs having a mild impact. Out of twenty-three tested compounds, eight significantly reduced ACE2 maturation levels, and three caused approximately 20% decreases. Screening trafficking inhibitors revealed significant effects from most molecular modulators of protein trafficking, mild effects from most proposed COVID-19 drugs, and no effects from statins. This study noted that manipulating ACE2 levels could be beneficial or harmful, depending on the context. Thus, using this approach to uncover leads for COVID-19 therapeutics requires a thorough understanding ACE2's biogenesis and biology.

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.

Gut microbiota-derived metabolites contribute negatively to hindgut barrier function development at the early weaning goat model

Early weaning induces intestinal injury, leading to a series of long-term symptoms such as inflammation, malabsorption and diarrhea. In this study, we hypothesized that microbes and their metabolites modulate the host's inflammatory response to early weaning stress in a goat model. A total of 18 female Tibetan goat kids (n = 9) were weaned from their mothers at 28 d (D28) and 60 d (D60) postpartum. D60 and D28 groups were fed the same solid diet ad libitum from weaning to 75 d of age. The colonic epithelium was subject to RNA-sequencing, the caecal digesta metabolomics were assessed by liquid chromatography–tandem mass spectrometry (LC-MS/MS), and the caecal microbiota composition was analysed by 16S ribosomal RNA gene sequencing. We found that early weaning substantially increased the colonic pro-apoptotic gene expression of B-cell lymphoma associated X (Bax), caspase-9, and caspase-3, and decreased the expression of zonula occludens-1 (ZO-1) and claudin-1 (P < 0.01). In addition, a significant Bacteroides acidifaciens enrichment was observed in the hindgut of early-weaned goats (P < 0.01), which negatively correlated with lysophosphatidylcholine products. Similarly, the chemokine signaling, IL-17 signaling, and peroxisome proliferators-activated receptor (PPAR) signaling pathways were upregulated in the colonic mucosa of the early-weaned goats. By applying caecal microbiota transplantation from goats to defaunated C57/6J mice, we confirmed that caecal microbiota of D28 goat kids increased the relative abundance of B. acidifaciens and significantly up-regulated the genes of Bax, G protein–coupled receptor (GPR) 109A, GPR 43, fatty acid binding protein 6, nuclear receptor subfamily 1 group H member 3, angiotensin converting enzyme 2, and IL-6 expression (P < 0.05), and decreased ZO-1, and claudin-1 protein expression in the mice jejunum and colon (P < 0.001). These results proposed that the hindgut microbiota and metabolites mediate the barrier function weakening during early weaning, and the relative abundance of B. acidifaciens was negatively correlated with the hindgut barrier gene expression. This study demonstrates how weaning stress can affect key host–microbe interaction regulators in the hindgut, in a lysophosphatidylcholine dependent and independent manner. Furthermore, based on our mice data, these results are transferable to other mammal species.

Simian Immunodeficiency Virus Infection Mediated Changes in Jejunum and Peripheral SARS-CoV-2 Receptor ACE2 and Associated Proteins or Genes in Rhesus Macaques

Angiotensin converting enzyme-2 (ACE2) and associated proteins play a pivotal role in various physiological and pathological events, such as immune activation, inflammation, gut barrier maintenance, intestinal stem cell proliferation, and apoptosis. Although many of these clinical events are quite significant in SIV/HIV infection, expression profiling of these proteins has not been well reported. Considering the different pathological consequences in the gut after HIV infection, we hypothesized that the expression of ACE2 and associated proteins of the Renin-angiotensin system (RAS) could be compromised after SIV/HIV infection. We quantified the gene expression of ACE2 as well as AGTR1/2, ADAM17, and TMPRSS2, and compared between SIV infected and uninfected rhesus macaques (Macaca mulatta; hereafter abbreviated RMs). The gene expression analysis revealed significant downregulation of ACE2 and upregulation of AGTR2 and inflammatory cytokine IL-6 in the gut of infected RMs. Protein expression profiling also revealed significant upregulation of AGTR2 after infection. The expression of ACE2 in protein level was also decreased, but not significantly, after infection. To understand the entirety of the process in newly regenerated epithelial cells, a global transcriptomic study of enteroids raised from intestinal stem cells was performed. Interestingly, most of the genes associated with the RAS, such as DPP4, MME, ANPEP, ACE2, ENPEP, were found to be downregulated in SIV infection. HNFA1 was found to be a key regulator of ACE2 and related protein expression. Jejunum CD4+ T cell depletion and increased IL-6 mRNA, MCP-1 and AGTR2 expression may signal inflammation, monocyte/macrophage accumulation and epithelial apoptosis in accelerating SIV pathogenesis. Overall, the findings in the study suggested a possible impact of SIV/HIV infection on expression of ACE2 and RAS-associated proteins resulting in the loss of gut homeostasis. In the context of the current COVID-19 pandemic, the outcome of SARS-CoV-2 and HIV co-infection remains uncertain and needs further investigation as the significance profile of ACE2, a viral entry receptor for SARS-CoV-2, and its expression in mRNA and protein varied in the current study. There is a concern of aggravated SARS-CoV-2 outcomes due to possible serious pathological events in the gut resulting from compromised expression of RAS- associated proteins in SIV/HIV infection.

SARS-CoV-2-host cell surface interactions and potential antiviral therapies

In this review, we reveal the latest developments at the interface between SARS-CoV-2 and the host cell surface. In particular, we evaluate the current and potential mechanisms of binding, fusion and the conformational changes of the spike (S) protein to host cell surface receptors, especially the human angiotensin-converting enzyme 2 (ACE2) receptor. For instance, upon the initial attachment, the receptor binding domain of the S protein forms primarily hydrogen bonds with the protease domain of ACE2 resulting in conformational changes within the secondary structure. These surface interactions are of paramount importance and have been therapeutically exploited for antiviral design, such as monoclonal antibodies. Additionally, we provide an insight into novel therapies that target viral non-structural proteins, such as viral RNA polymerase. An example of which is remdesivir which has now been approved for use in COVID-19 patients by the US Food and Drug Administration. Establishing further understanding of the molecular details at the cell surface will undoubtably aid the development of more efficacious and selectively targeted therapies to reduce the burden of COVID-19.

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.

Interactions between the Gut Microbiome, Lung Conditions, and Coronary Heart Disease and How Probiotics Affect These

The importance of a healthy microbiome cannot be overemphasized. Disturbances in its composition can lead to a variety of symptoms that can extend to other organs. Likewise, acute or chronic conditions in other organs can affect the composition and physiology of the gut microbiome. Here, we discuss interorgan communication along the gut–lung axis, as well as interactions between lung and coronary heart diseases and between cardiovascular disease and the gut microbiome. This triangle of organs, which also affects the clinical outcome of COVID-19 infections, is connected by means of numerous receptors and effectors, including immune cells and immune-modulating factors such as short chain fatty acids (SCFA) and trimethlamine–N–oxide (TMAO). The gut microbiome plays an important role in each of these, thus affecting the health of the lungs and the heart, and this interplay occurs in both directions. The gut microbiome can be influenced by the oral uptake of probiotics. With an improved understanding of the mechanisms responsible for interorgan communication, we can start to define what requirements an ‘ideal’ probiotic should have and its role in this triangle.

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.

Percutaneous microwave ablation applications for liver tumors: recommendations for COVID-19 patients

Microwave ablation (MWA) is an alternative locoregional therapy to surgical resection of solid tumors in the treatment of malignancies, and is widely used for hepatic tumors. It has a slightly higher overall survival (OS) rate compared to external beam radiation therapy (EBRT), and proton beam therapy (PBT), and better long-term recurrence-free OS rate compared to radiofrequency ablation (RFA). In this paper, current commercial devices, most recent noncommercial designs, and the principles behind them alongside the recently reported developments and issues of MWA are reviewed. The paper also provides microscopic insights on effects of microwave irradiation in the body. Our review shows that MWA is a safe and effective, minimally invasive method with high ablation completion rates. However, for large tumors, the completion rates slightly decrease, and recurrences increase. Thus, for large tumors we suggest using a cooled shaft antenna or multiple antenna placements. Comparisons of the two common ablation frequencies 915 MHz and 2.45 GHz have shown inconsistent results due to non-identical conditions. This review suggests that 915 MHz devices are more effective for ablating large tumors and the theory behind MWA effects corroborates this proposition. However, for small tumors or tumors adjacent to vital organs, 2.45 GHz is suggested due to its more localized ablation zone. Among the antenna designs, the double-slot antenna with a metallic choke seems to be more effective by localizing the radiation around the tip of the antenna, while also preventing backward radiation towards the skin. The review also pertains to the use of MWA in COVID-19 patients and risk factors associated with the disease. MWA should be considered for COVID-19 patients with hepatic tumors as a fast treatment with a short recovery time. As liver injury is also a risk due to COVID-19, it is recommended to apply liver function tests to monitor abnormal levels in alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin, and other liver function indicators.

Management of inflammatory bowel disease in the COVID-19 era

During the coronavirus disease 2019 (COVID-19) pandemic, many unpredictable changes have occurred in the medical field. Risk of COVID-19 does not seem to increase in patients with inflammatory bowel disease (IBD) considering based on current reports. Current medications for IBD do not increase this risk; on the contrary, some of these might be used as therapeutics against COVID-19 and are under clinical trial. Unless the patients have confirmed COVID-19 and severe pneumonia or a high oxygen demand, medical treatment should be continued during the pandemic, except for the use of high-dose corticosteroids. Adherence to general recommendations such as social distancing, wearing facial masks, and vaccination, especially for pneumococcal infections and influenza, is also required. Patients with COVID-19 need to be withhold immunomodulators or biologics for at least 2 weeks and treated based on both IBD and COVID-19 severity. Prevention of IBD relapse caused by sudden medication interruption is important because negative outcomes associated with disease flare up, such as corticosteroid use or hospitalization, are much riskier than medications. The outpatient clinic and infusion center for biologics need to be reserved safe spaces, and endoscopy or surgery should be considered in urgent cases only.

Potential detrimental role of soluble ACE2 in severe COVID-19 comorbid patients

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters the host cell by binding to angiotensin-converting enzyme 2 (ACE2) receptor. Other important proteins involved in this process include disintegrin and metalloproteinase domain-containing protein 17 (ADAM17) also known as tumour necrosis factor-α-converting enzyme and transmembrane serine protease 2. ACE2 converts angiotensin II (Ang II) to angiotensin (1-7), to balance the renin angiotensin system. Membrane-bound ACE2 ectodomain shedding is mediated by ADAM17 upon viral spike binding, Ang II overproduction and in several diseases. The shed soluble ACE2 (sACE2) retains its catalytic activity, but its precise role in viral entry is still unclear. Therapeutic sACE2 is claimed to exert dual effects; reduction of excess Ang II and blocking viral entry by masking the spike protein. Nevertheless, the paradox is why SARS-CoV-2 comorbid patients struggle to attain such benefit in viral infection despite having a high amount of sACE2. In this review, we discuss the possible detrimental role of sACE2 and speculate on a series of events where protease primed or non-primed virus-sACE2 complex might enter the host cell. As extracellular virus can bind many sACE2 molecules, sACE2 level could be reduced drastically upon endocytosis by the host cell. A consequential rapid rise in Ang II level could potentially aggravate disease severity through Ang II-angiotensin II receptor type 1 (AT1R) axis in comorbid patients. Hence, monitoring sACE2 and Ang II level in coronavirus disease 2019 comorbid patients are crucial to ensure safe and efficient intervention using therapeutic sACE2 and vaccines.

ACE2: the molecular doorway to SARS-CoV-2

The angiotensin-converting enzyme 2 (ACE2) is the host functional receptor for the new virus SARS-CoV-2 causing Coronavirus Disease 2019. ACE2 is expressed in 72 different cell types. Some factors that can affect the expression of the ACE2 are: sex, environment, comorbidities, medications (e.g. anti-hypertensives) and its interaction with other genes of the renin-angiotensin system and other pathways. Different factors can affect the risk of infection of SARS-CoV-2 and determine the severity of the symptoms. The ACE2 enzyme is a negative regulator of RAS expressed in various organ systems. It is with immunity, inflammation, increased coagulopathy, and cardiovascular disease. In this review, we describe the genetic and molecular functions of the ACE2 receptor and its relation with the physiological and pathological conditions to better understand how this receptor is involved in the pathogenesis of COVID-19. In addition, it reviews the different comorbidities that interact with SARS-CoV-2 in which also ACE2 plays an important role. It also describes the different factors that interact with the virus that have an influence in the expression and functional activities of the receptor. The goal is to provide the reader with an understanding of the complexity and importance of this receptor.