Angiotensin converting enzyme 2 abrogates bleomycin-induced lung injury

Mathematical modeling of impacts of patient differences on renin-angiotensin system and applications to COVID-19 lung fibrosis outcomes

Patient-specific premorbidity, age, and sex are significant heterogeneous factors that influence the severe manifestation of lung diseases, including COVID-19 fibrosis. The renin-angiotensin system (RAS) plays a prominent role in regulating the effects of these factors. Recent evidence shows patient-specific alterations of RAS peptide homeostasis concentrations with premorbidity and the expression level of angiotensin-converting enzyme 2 (ACE2) during COVID-19. However, conflicting evidence suggests decreases, increases, or no changes in RAS peptides after SARS-CoV-2 infection. A multiscale computational model was developed to quantify the systemic contribution of heterogeneous factors of RAS during COVID-19. Three submodels were connected-an agent-based model for in-host COVID-19 response in the lung tissue, a RAS dynamics model, and a fibrosis dynamics model to investigate the effects of patient-group-specific factors in the systemic alteration of RAS and collagen deposition in the lung. The model results indicated cell death due to inflammatory response as a major contributor to the reduction of ACE and ACE2. The model explained possible mechanisms for conflicting evidence of patient-group-specific changes in RAS peptides in previously published studies. RAS peptides decreased for all virtual patient groups with aging in both sexes. In contrast, large variations in the magnitude of reduction were observed between male and female virtual patients in the older and middle-aged groups. The patient-specific variations in homeostasis RAS peptide concentrations of SARS-CoV-2-negative patients affected the dynamics of RAS during infection. This model may find further applications in patient-specific calibrations of tissue models for acute and chronic lung diseases to develop personalized treatments.

The renin-angiotensin-aldosterone system: An old tree sprouts new shoots

The intricate physiological and pathological diversity of the Renin-Angiotensin-Aldosterone System (RAAS) underpins its role in maintaining bodily equilibrium. This paper delves into the classical axis (Renin-ACE-Ang II-AT1R axis), the protective arm (ACE2-Ang (1-7)-MasR axis), the prorenin-PRR-MAP kinases ERK1/2 axis, and the Ang IV-AT4R-IRAP cascade of RAAS, examining their functions in both physiological and pathological states. The dysregulation or hyperactivation of RAAS is intricately linked to numerous diseases, including cardiovascular disease (CVD), renal damage, metabolic disease, eye disease, Gastrointestinal disease, nervous system and reproductive system diseases. This paper explores the pathological mechanisms of RAAS in detail, highlighting its significant role in disease progression. Currently, in addition to traditional drugs like ACEI, ARB, and MRA, several novel therapeutics have emerged, such as angiotensin receptor-enkephalinase inhibitors, nonsteroidal mineralocorticoid receptor antagonists, aldosterone synthase inhibitors, aminopeptidase A inhibitors, and angiotensinogen inhibitors. These have shown potential efficacy and application prospects in various clinical trials for related diseases. Through an in-depth analysis of RAAS, this paper aims to provide crucial insights into its complex physiological and pathological mechanisms and offer valuable guidance for developing new therapeutic approaches. This comprehensive discussion is expected to advance the RAAS research field and provide innovative ideas and directions for future clinical treatment strategies.

Mathematical Modeling of Impacts of Patient Differences on Renin-Angiotensin System and Applications to COVID-19 Lung Fibrosis Outcomes

Patient-specific premorbidity, age, and sex are significant heterogeneous factors that influence the severe manifestation of lung diseases, including COVID-19 fibrosis. The renin-angiotensin system (RAS) plays a prominent role in regulating the effects of these factors. Recent evidence shows patient-specific alterations of RAS homeostasis concentrations with premorbidity and the expression level of angiotensin-converting enzyme 2 (ACE2) during COVID-19. However, conflicting evidence suggests decreases, increases, or no changes in RAS peptides after SARS-CoV-2 infection. In addition, detailed mechanisms connecting the patient-specific conditions before infection to infection-induced RAS alterations are still unknown. Here, a multiscale computational model was developed to quantify the systemic contribution of heterogeneous factors of RAS during COVID-19. Three submodels were connected-an agent-based model for in-host COVID-19 response in the lung tissue, a RAS dynamics model, and a fibrosis dynamics model to investigate the effects of patient-group-specific factors in the systemic alteration of RAS and collagen deposition in the lung. The model results indicated cell death due to inflammatory response as a major contributor to the reduction of ACE and ACE2. In contrast, there were no significant changes in ACE2 dynamics due to viral-bound internalization of ACE2. The model explained possible mechanisms for conflicting evidence of patient-group-specific changes in RAS peptides in previously published studies. Simulated results were consistent with reported RAS peptide values for SARS-CoV-2-negative and SARS-CoV-2-positive patients. RAS peptides decreased for all virtual patient groups with aging in both sexes. In contrast, large variations in the magnitude of reduction were observed between male and female virtual patients in the older and middle-aged groups. The patient-specific variations in homeostasis RAS peptide concentrations of SARS-CoV-2-negative patients also affected the dynamics of RAS during infection. The model results also showed that feedback between RAS signaling and renin dynamics could restore ANGI homeostasis concentration but failed to restore homeostasis values of RAS peptides downstream of ANGI. In addition, the results showed that ACE2 variations with age and sex significantly altered the concentrations of RAS peptides and led to collagen deposition with slight variations depending on age and sex. This model may find further applications in patient-specific calibrations of tissue models for acute and chronic lung diseases to develop personalized treatments.

Characterization of an engineered ACE2 protein for its improved biological features and its transduction into MSCs: A novel approach to combat COVID-19 infection

Transduced MSCs that express engineered ACE2 could be highly beneficial to combat COVID-19. Engineered ACE2 can act as decoy targets for the virus, preventing its entry into healthy lung cells. To this end, genetic engineering techniques were used to integrate the ACE2 gene into the MSCs genome. The MSCs were evaluated for proper expression and functionality. The mutated form of ACE2 was characterized using various techniques such as protein expression analysis, binding affinity against spike protein, thermal stability assessment, and enzymatic activity assays. The functionality of the mACE2 was assessed on SARS-CoV-2 using the virus-neutralizing test. The obtained results indicated that by introducing specific mutations in the ACE2 gene, the resulting mutant ACE2 had enhanced interaction with viral spike protein, its thermal stability was increased, and its enzymatic function was inhibited as a decoy receptor. Moreover, the mACE2 protein showed higher efficacy in the neutralization of the SARS-CoV-2. In conclusion, this study proposes a novel approach with potential benefits such as targeted drug delivery and reduced side effects on healthy tissues. These transduced MSCs can also be used in combination with other anti-COVID-19 treatments. Design of similar engineered biomolecules with desired properties could also be used to target other diseases.

Angiotensin-(1-7) infusion in COVID-19 patients admitted to the ICU: a seamless phase 1-2 randomized clinical trial

BACKGROUND

The coronavirus-related disease (COVID-19) is mainly characterized by a respiratory involvement. The renin-angiotensin system (RAS) has a relevant role in the pathogenesis of COVID-19, as the virus enters host's cells via the angiotensin-converting enzyme 2 (ACE2).

METHODS

This investigator-initiated, seamless phase 1-2 randomized clinical trial was conceived to test the safety and efficacy of continuous short-term (up to 7 days) intravenous administration of Angiotensin-(1-7) in COVID-19 patients admitted to two intensive care units (ICU). In addition to standard of care, intravenous administration of Angiotensin-(1-7) was started at 5 mcg/Kg day and increased to 10 mcg/Kg day after 24 h (Phase 1; open label trial) or given at 10 mcg/Kg day and continued for a maximum of 7 days or until ICU discharge (Phase 2; double-blind randomized controlled trial). The rate of serious adverse events (SAEs) served as the primary outcome of the study for Phase 1, and the number of oxygen free days (OFDs) by day 28 for Phase 2.

RESULTS

Between August 2020 and July 2021, when the study was prematurely stopped due to low recruitment rate, 28 patients were included in Phase 1 and 79 patients in Phase 2. Of those, 78 were included in the intention to treat analysis, and the primary outcome was available for 77 patients. During Phase 1, one SAE (i.e., bradycardia) was considered possibly related to the infusion, justifying its discontinuation. In Phase 2, OFDs did not differ between groups (median 19 [0-21] vs. 14 [0-18] days; p = 0.15). When patients from both phases were analyzed in a pooled intention to treat approach (Phase 1-2 trial), OFDs were significantly higher in treated patients, when compared to controls (19 [0-21] vs. 14 [0-18] days; absolute difference -5 days, 95% CI [0-7] p = 0.04).

CONCLUSIONS

The main findings of our study indicate that continuous intravenous infusion of Angiotensin-(1-7) at 10 mcg/Kg day in COVID-19 patients admitted to the ICU with severe pneumonia is safe. In Phase II intention to treat analysis, there was no significant difference in OFD between groups. Trial Registration ClinicalTrials.gov Identifier: NCT04633772-Registro Brasileiro de Ensaios Clínicos, UTN number: U1111-1255-7167.

A cardiotoxicity-eliminated ACE2 variant as a pan-inhibitor against coronavirus cell invasion

Human recombinant ACE2 (hrACE2) has been highly anticipated as a successful COVID-19 treatment; however, its potential to cause cardiac side effects has given rise to many concerns. Here, we developed a cardiotoxicity-eliminated hrACE2 variant, which had four mutation sites within hrACE2 (H345L, H374L, H378L, H505L) and was named as hrACE2-4mu. hrACE2-4mu has a consistent binding affinity with the variant SARS-CoV-2 spike proteins (SPs) and an efficient ability to block SP-induced SARS-CoV-2 entry into cells. In golden hamsters, injection of purified wild-type (WT) hrACE2 rescues the early stages of pneumonia caused by the SPs of the WT, delta, and omicron variants with reduced inflammatory cell infiltration. However, long-term injection of WT hrACE2 induces undesired cardiac fibrosis, as demonstrated by upregulated fibronectin and collagen expression. Our newly developed hrACE2-4mu showed similar protective abilities against a series of coronavirus cell invasions as WT hrACE2, meanwhile it did not cause apparent cardiac side effects. Thus, we generated a cardiotoxicity-eliminated variant of hrACE2 as a pan-inhibitor against coronavirus cell invasion, providing a potential novel strategy for the treatment of COVID-19 and other coronaviruses.

Targeting the renin angiotensin system for respiratory diseases

Renin-angiotensin system (RAS) plays an indispensable role in regulating blood pressure through its effects on fluid and electrolyte balance. As an aside, cumulative evidence from experimental to clinical studies supports the notion that dysregulation of RAS contributes to the pro-inflammatory, pro-oxidative, and pro-fibrotic processes that occur in pulmonary diseases like asthma, chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), and acute lung injury (ALI). Pharmacological intervention of the various RAS components can be a novel therapeutic strategy for the treatment of these respiratory diseases. In this chapter, we first give a recent update on the RAS, and then compile, review, and analyse recent reports on targeting RAS components as treatments for respiratory diseases. Inhibition of the pro-inflammatory renin, angiotensin-converting enzyme (ACE), angiotensin (Ang) II, and Ang II type 1 receptor (AT1R) axis, and activation of the protective ACE2, AT2R, Ang (1-7), and Mas receptor axis have demonstrated varying degrees of efficacies in experimental respiratory disease models or in human trials. The newly identified alamandine/Mas-related G-protein-coupled receptor member D pathway has shown some therapeutic promise as well. However, our understanding of the RAS ligand-and-receptor interactions is still inconclusive, and the modes of action and signaling cascade mediating the newly identified RAS receptors remain to be better characterized. Clinical data are obviously lacking behind the promising pre-clinical findings of certain well-established molecules targeting at different pathways of the RAS in respiratory diseases. Translational human studies should be the focus for RAS drug development in lung diseases in the next decade.

SARS-CoV-2 leverages airway epithelial protective mechanism for viral infection

Despite much concerted effort to better understand severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral infection, relatively little is known about the dynamics of early viral entry and infection in the airway. Here we analyzed a single-cell RNA sequencing dataset of early SARS-CoV-2 infection in a humanized in vitro model, to elucidate key mechanisms by which the virus triggers a cell-systems-level response in the bronchial epithelium. We find that SARS-CoV-2 virus preferentially enters the tissue via ciliated cell precursors, giving rise to a population of infected mature ciliated cells, which signal to basal cells, inducing further rapid differentiation. This feedforward loop of infection is mitigated by further cell-cell communication, before interferon signaling begins at three days post-infection. These findings suggest hijacking by the virus of potentially beneficial tissue repair mechanisms, possibly exacerbating the outcome. This work both elucidates the interplay between barrier tissues and viral infections and may suggest alternative therapeutic approaches targeting non-immune response mechanisms.

Counter-regulatory renin-angiotensin system in hypertension: Review and update in the era of COVID-19 pandemic

Cardiovascular disease is the major cause of mortality and disability, with hypertension being the most prevalent risk factor. Excessive activation of the renin-angiotensin system (RAS) under pathological conditions, leading to vascular remodeling and inflammation, is closely related to cardiovascular dysfunction. The counter-regulatory axis of the RAS consists of angiotensin-converting enzyme 2 (ACE2), angiotensin (1-7), angiotensin (1-9), alamandine, proto-oncogene Mas receptor, angiotensin II type-2 receptor and Mas-related G protein-coupled receptor member D. Each of these components has been shown to counteract the effects of the overactivated RAS. In this review, we summarize the latest insights into the complexity and interplay of the counter-regulatory RAS axis in hypertension, highlight the pathophysiological functions of ACE2, a multifunctional molecule linking hypertension and COVID-19, and discuss the function and therapeutic potential of targeting this counter-regulatory RAS axis to prevent and treat hypertension in the context of the current COVID-19 pandemic.

Thymosin β4 and the anti-fibrotic switch

Wound healing involves a rapid response to the injury by circulating cells, followed by inflammation with an influx of inflammatory cells that release various factors. Soon after, cellular proliferation begins to replace the damaged cells and extracellular matrix, and then tissue remodeling restores normal tissue function. Various factors can lead to pathological wound healing when excessive and irreversible connective tissue/extracellular matrix deposition occurs, resulting in fibrosis. The process is initiated when immune cells, such as macrophages, release soluble factors that stimulate fibroblasts. TGFβ is the most well-characterized macrophage derived pro-fibrotic mediator. Other soluble mediators of fibrosis include connective tissue growth factor (CTGF), platelet-derived growth factor (PDGF), and interleukin 10 (IL-10). Thymosin β4 (Tβ4) has shown therapeutic benefit in preventing fibrosis/scarring in various animal models of fibrosis/scarring. The mechanism of action of Tβ4 appears related, in part, to a reduction in the inflammatory response, including a reduction in macrophage infiltration, decreased levels of TGFβ and IL-10, and reduced CTGF activation, resulting in both prevention of fibroblast conversion to myofibroblasts and production of normally aligned collagen fibers. The amino N-terminal end of Tβ4, SDKP (serine-aspartate-lysine-proline), appears to contain the majority of anti-fibrotic activity and has shown excellent efficacy in many animal models of fibrosis, including liver, lung, heart, and kidney fibrosis. Ac-SDKP not only prevents fibrosis but can reverse fibrosis. Unanswered questions and future directions will be presented with regard to therapeutic uses alone and in combination with already approved drugs for fibrosis.

Estrogens as a Possible Therapeutic Strategy for the Management of Neuroinflammation and Neuroprotection in COVID-19

The Coronavirus disease 2019 (COVID-19) affects several tissues, including the central and peripheral nervous system. It has also been related to signs and symptoms that suggest neuroinflammation with possible effects in the short, medium, and long term. Estrogens could have a positive impact on the management of the disease, not only due to its already known immunomodulator effect, but also activating other pathways that may be important in the pathophysiology of COVID-19, such as the regulation of the virus receptor and its metabolites. In addition, they can have a positive effect on neuroinflammation secondary to pathologies other than COVID-19. The aim of this study is to analyze the molecular mechanisms that link estrogens with their possible therapeutic effect for neuroinflammation related to COVID-19. Advanced searches were performed in scientific databases as Pub- Med, ProQuest, EBSCO, the Science Citation index, and clinical trials. Estrogens have been shown to participate in the immune modulation of the response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In addition to this mechanism, we propose that estrogens can regulate the expression and activity of the Angiotensin-converting enzyme 2 (ACE2), reestablishing its cytoprotective function, which may be limited by its interaction with SARS-CoV-2. In this proposal, estrogens and estrogenic compounds could increase the synthesis of Angiotensin-(1-7) (Ang-(1-7)) that acts through the Mas receptor (MasR) in cells that are being attacked by the virus. Estrogens can be a promising, accessible, and low-cost treatment for neuroprotection and neuroinflammation in patients with COVID-19, due to its direct immunomodulatory capacity in decreasing cytokine storm and increasing cytoprotective capacity of the axis ACE2/Ang (1-7)/MasR.

Pathophysiological conditions induced by SARS-CoV-2 infection reduce ACE2 expression in the lung

SARS-CoV-2 infection causes a variety of physiological responses in the lung, and understanding how the expression of SARS-CoV-2 receptor, angiotensin-converting enzyme 2 (ACE2), and its proteolytic activator, transmembrane serine protease 2 (TMPRSS2), are affected in patients with underlying disease such as interstitial pneumonia will be important in considering COVID-19 progression. We examined the expression of ACE2 and TMPRSS2 in an induced usual interstitial pneumonia (iUIP) mouse model and patients with IPF as well as the changes in whole-lung ACE2 and TMPRSS2 expression under physiological conditions caused by viral infection. Histopathological and biochemical characteristics were analyzed using human specimens from patients with IPF and precision-cut lung slices (PCLS) from iUIP mouse model showing UIP with honeycombing and severe fibrosis after non-specific interstitial pneumonia. ACE2 expression decreased with acute lung inflammation and increased in the abnormal lung epithelium of the iUIP mouse model. ACE2 is also expressed in metaplastic epithelial cells. Poly(I:C), interferons, and cytokines associated with fibrosis decreased ACE2 expression in PCLS in the iUIP model. Hypoxia also decreases ACE2 via HIF1α in PCLS. Antifibrotic agent, nintedanib attenuates ACE2 expression in invasive epithelial cells. Patients with IPF are at a higher risk of SARS-CoV-2 infection due to the high expression of ACE2. However, ACE2 and TMPRSS2 expression is decreased by immune intermediaries, including interferons and cytokines that are associated with viral infection and upon administration of antifibrotic agents, suggesting that most of the viral infection-induced pathophysiological responses aid the development of resistance against SARS-CoV-2 infection.

[Angiotensin-converting enzyme 2 particapates in ozone-induced lung inflammation and airway remodeling in mice]

OBJECTIVE

To investigate the roles of angiotensin-converting enzyme 2 (ACE2) in ozone-induced pulmonary inflammation and airway remodeling in mice.

METHODS

Sixteen wild-type (WT) C57BL/6J mice and 16 ACE2 knock-out (KO) mice were exposed to either filtered air or ozone (0.8 ppm) for 3 h per day for 5 consecutive days. Masson's staining and HE staining were used to observe lung pathologies. Bronchoalveolar lavage fluid (BALF) was collected and the total cell count was determined. The total proteins and cytokines in BALF were determined by BCA and ELISA method. The transcription levels of airway remodeling-related indicators in the lung tissues were detected using real-time quantitative PCR. The airway resistance of the mice was measured using a small animal ventilator with methacholine stimulation.

RESULTS

Following ozoneexposure ACE2 KO mice had significantly higher lung pathological scores than WT mice (P < 0.05). Masson staining results showed that compared with ozone-exposed WT mice, ozone-exposed ACE2 KO mice presented with significantly larger area of collagen deposition in the bronchi [(19.62±3.16)% vs (6.49±1.34)%, P < 0.05] and alveoli [(21.63±3.78)% vs (4.44±0.99)%, P < 0.05]. The total cell count and total protein contents in the BALF were both higher in ozone-exposed ACE2 KO mice than in WT mice, but these differences were not statistically significant (P > 0.05). The concentrations of IL-6, IL-1β, TNF-α, CXCL1/KC and MCP-1 in the BALF were all higher in ozone-exposed ACE2 KO mice than in ozone-exposed WT mice, but only the difference in IL-1β was statistically significant (P < 0.05). The transcription levels of MMP-9, MMP-13, TIMP 4, COL1A1, and TGF-β in the lung tissues were all significantly higher in ozone-exposed ACE2 KO mice (P < 0.01). No significant difference was found in airway resistance between ozone-exposed ACE KO mice and WT mice after challenge with 0, 10, 25, or 100 mg/mL of methacholine.

CONCLUSION

ACE2 participates in ozone-induced lung inflammation and airway remodeling in mice.

Danshensu alleviates pseudo-typed SARS-CoV-2 induced mouse acute lung inflammation

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can induce acute inflammatory response like acute lung inflammation (ALI) or acute respiratory distress syndrome, leading to severe progression and mortality. Therapeutics for treatment of SARS-CoV-2-triggered respiratory inflammation are urgent to be discovered. Our previous study shows that Salvianolic acid C potently inhibits SARS-CoV-2 infection. In this study, we investigated the antiviral effects of a Salvia miltiorrhiza compound, Danshensu, in vitro and in vivo, including the mechanism of S protein-mediated virus attachment and entry into target cells. In authentic and pseudo-typed virus assays in vitro, Danshensu displayed a potent antiviral activity against SARS-CoV-2 with EC₅₀ of 0.97 μM, and potently inhibited the entry of SARS-CoV-2 S protein-pseudo-typed virus (SARS-CoV-2 S) into ACE2-overexpressed HEK-293T cells (IC₅₀ = 0.31 μM) and Vero-E6 cell (IC₅₀ = 4.97 μM). Mice received SARS-CoV-2 S via trachea to induce ALI, while the VSV-G treated mice served as controls. The mice were administered Danshensu (25, 50, 100 mg/kg, i.v., once) or Danshensu (25, 50, 100 mg·kg^-1·d^-1, oral administration, for 7 days) before SARS-CoV-2 S infection. We showed that SARS-CoV-2 S infection induced severe inflammatory cell infiltration, severely damaged lung tissue structure, highly expressed levels of inflammatory cytokines, and activated TLR4 and hyperphosphorylation of the NF-κB p65; the high expression of angiotensinogen (AGT) and low expression of ACE2 at the mRNA level in the lung tissue were also observed. Both oral and intravenous pretreatment with Danshensu dose-dependently alleviated the pathological alterations in mice infected with SARS-CoV-2 S. This study not only establishes a mouse model of pseudo-typed SARS-CoV-2 (SARS-CoV-2 S) induced ALI, but also demonstrates that Danshensu is a potential treatment for COVID-19 patients to inhibit the lung inflammatory response.

Angiotensin-converting enzyme 2: a key enzyme in key organs

2020 marked the 20th anniversary of the discovery of the angiotensin-converting enzyme 2 (ACE2). This major event that changed the way we see the renin-angiotensin system today could have passed quietly. Instead, the discovery that ACE2 is a major player in the severe acute respiratory syndrome coronavirus 2 pandemic has blown up the literature regarding this enzyme. ACE2 connects the classical arm renin-angiotensin system, consisting mainly of angiotensin II peptide and its AT1 receptor, with a protective arm, consisting mainly of the angiotensin 1-7 peptide and its Mas receptor. In this brief article, we have reviewed the literature to describe how ACE2 is a key protective arm enzyme in the function of many organs, particularly in the context of brain and cardiovascular function, as well as in renal, pulmonary and digestive homeostasis. We also very briefly review and refer to recent literature to present an insight into the role of ACE2 in determining the course of coronavirus diseases 2019.

Alternative RAS in Various Hypoxic Conditions: From Myocardial Infarction to COVID-19

Alternative branches of the classical renin–angiotensin–aldosterone system (RAS) represent an important cascade in which angiotensin 2 (AngII) undergoes cleavage via the action of the angiotensin-converting enzyme 2 (ACE2) with subsequent production of Ang(1-7) and other related metabolites eliciting its effects via Mas receptor activation. Generally, this branch of the RAS system is described as its non-canonical alternative arm with counterbalancing actions to the classical RAS, conveying vasodilation, anti-inflammatory, anti-remodeling and anti-proliferative effects. The implication of this branch was proposed for many different diseases, ranging from acute cardiovascular conditions, through chronic respiratory diseases to cancer, nonetheless, hypoxia is one of the most prominent common factors discussed in conjugation with the changes in the activity of alternative RAS branches. The aim of this review is to bring complex insights into the mechanisms behind the various forms of hypoxic insults on the activity of alternative RAS branches based on the different duration of stimuli and causes (acute vs. intermittent vs. chronic), localization and tissue (heart vs. vessels vs. lungs) and clinical relevance of studied phenomenon (experimental vs. clinical condition). Moreover, we provide novel insights into the future strategies utilizing the alternative RAS as a diagnostic tool as well as a promising pharmacological target in serious hypoxia-associated cardiovascular and cardiopulmonary diseases.

ACE2 and Innate Immunity in the Regulation of SARS-CoV-2-Induced Acute Lung Injury: A Review

Despite the protracted battle against coronavirus acute respiratory infection (COVID-19) and the rapid evolution of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), no specific and effective drugs have to date been reported. Angiotensin-converting enzyme 2 (ACE2) is a zinc metalloproteinase and a critical modulator of the renin-angiotensin system (RAS). In addition, ACE2 has anti-inflammatory and antifibrosis functions. ACE has become widely known in the past decade as it has been identified as the primary receptor for SARS-CoV and SARS-CoV-2, being closely associated with their infection. SARS-CoV-2 primarily targets the lung, which induces a cytokine storm by infecting alveolar cells, resulting in tissue damage and eventually severe acute respiratory syndrome. In the lung, innate immunity acts as a critical line of defense against pathogens, including SARS-CoV-2. This review aims to summarize the regulation of ACE2, and lung host cells resist SARS-CoV-2 invasion by activating innate immunity response. Finally, we discuss ACE2 as a therapeutic target, providing reference and enlightenment for the clinical treatment of COVID-19.

Renin angiotensin aldosterone system in pulmonary fibrosis: Pathogenesis to therapeutic possibilities

Pulmonary fibrosis is a devastating lung disease with multifactorial etiology characterized by alveolar injury, fibroblast proliferation and excessive deposition of extracellular matrix proteins, which progressively results in respiratory failure and death. Accumulating evidence from experimental and clinical studies supports a central role of the renin angiotensin aldosterone system (RAAS) in the pathogenesis and progression of idiopathic pulmonary fibrosis. Angiotensin II (Ang II), a key vasoactive peptide of the RAAS mediates pro-inflammatory and pro-fibrotic effects on the lungs, adversely affecting organ function. Recent years have witnessed seminal discoveries in the field of RAAS. Identification of new enzymes, peptides and receptors has led to the development of several novel concepts. Of particular interest is the establishment of a protective axis of the RAAS comprising of Angiotensin converting enzyme 2 (ACE2), Angiotensin-(1-7) [Ang-(1-7)], and the Mas receptor (the ACE2/Ang-(1-7)/Mas axis), and the discovery of a functional role for the Angiotensin type 2 (AT₂) receptor. Herein, we will review our current understanding of the role of RAAS in lung fibrogenesis, provide evidence on the anti-fibrotic actions of the newly recognized RAAS components (the ACE2/Ang-(1-7)/Mas axis and AT₂ receptor), discuss potential strategies and translational efforts to convert this new knowledge into effective therapeutics for PF.

ACE2 protein expression within isogenic cell lines is heterogeneous and associated with distinct transcriptomes

The membrane protein angiotensin-converting enzyme 2 (ACE2) is a physiologic regulator of the renin-angiotensin system and the cellular receptor for the SARS-CoV-2 virus. Prior studies of ACE2 expression have primarily focused on mRNA abundance, with investigation at the protein level limited by uncertain specificity of commercial ACE2 antibodies. Here, we report our development of a sensitive and specific flow cytometry-based assay for cellular ACE2 protein abundance. Application of this approach to multiple cell lines revealed an unexpected degree of cellular heterogeneity, with detectable ACE2 protein in only a subset of cells in each isogenic population. This heterogeneity was mediated at the mRNA level by transcripts predominantly initiated from the ACE2 proximal promoter. ACE2 expression was heritable but not fixed over multiple generations of daughter cells, with gradual drift toward the original heterogeneous background. RNA-seq profiling identified distinct transcriptomes of ACE2-expressing relative cells to non-expressing cells, with enrichment in functionally related genes and transcription factor target sets. Our findings provide a validated approach for the specific detection of ACE2 protein at the surface of single cells, support an epigenetic mechanism of ACE2 gene regulation, and identify specific pathways associated with ACE2 expression in HuH7 cells.

Expression of ACE2 in the Intact and Acutely Injured Kidney

Background

The actions of angiotensin-converting enzyme 2 (ACE2) oppose those of the renin-angiotensin-aldosterone system. ACE2 may be a cytoprotectant in some tissues. This study examined ACE2 expression in models of AKI.

Methods

ACE2 mRNA and protein expression and ACE2 activity were assessed in murine ischemic AKI. Renal ACE2 mRNA expression was evaluated in LPS-induced AKI in wild-type (C57BL/6J) mice, in heme oxygenase-1+/+ and heme oxygenase-1-/- mice, and after unilateral ureteral obstruction (UUO) in wild-type mice. The effect of sex and age on renal ACE2 protein expression was also assessed.

Results

In ischemic AKI, ACE2 mRNA and protein expression and ACE2 activity were reduced as compared with such indices in the intact kidney. In ischemic AKI, ACE2, which, in health, is prominently expressed in the tubular epithelium, especially proximal tubules, is decreased in expression in these segments. Decreased ACE2 expression in AKI did not reflect reduced GFR, because ACE2 mRNA expression was unaltered after UUO. LPS induced renal ACE2 mRNA expression in wild-type mice, but this effect did not occur in heme oxygenase-1-deficient mice. In ischemic and LPS-induced AKI, renal expression of the Mas receptor was increased. In the intact kidney, renal ACE2 protein expression decreased in female mice as compared with male mice, but was unaltered with age.

Conclusion

We conclude that renal ACE2 expression is decreased in ischemic AKI, characterized by decreased GFR and abundant cell death, but is upregulated in LPS-induced AKI, an effect requiring heme oxygenase-1. Determining the significance of ACE2 expression in experimental AKI merits further study. We suggest that understanding the mechanism underlying ACE2 downregulation in AKI may offer insights relevant to COVID-19: ACE2 expression is downregulated after ACE2 mediates SARS-CoV-2 cellular entry; such downregulation is proinflammatory; and AKI commonly occurs and determines outcomes in COVID-19.

Novel insights into the pathogenesis of virus-induced ARDS: review on the central role of the epithelial-endothelial barrier

Introduction: Respiratory viruses can directly or indirectly damage the pulmonary defense barrier, potentially contributing to acute respiratory distress syndrome (ARDS). Despite developments in the understanding of the pathogenesis of ARDS, the underlying pathophysiology still needs to be elucidated.Areas covered: The PubMed database was reviewed for relevant papers published up to 2021. This review summarizes the currently immunological and clinical studies to provide a systemic overview of the epithelial-endothelial barrier, given the recently published immunological profiles upon viral pneumonia, and the potentially detrimental contribution to respiratory function caused by damage to this barrier.Expert opinion: The biophysical structure of host pulmonary defense is intrinsically linked with the ability of alveolar epithelial and capillary endothelial cells, known as the epithelial-endothelial barrier, to respond to, and instruct the delicate immune system to protect the lungs from infections and injuries. Recently published immunological profiles upon viral infection, and its contributions to the damage of respiratory function, suggest a central role for the pulmonary epithelial and endothelial barrier in the pathogenesis of ARDS. We suggest a central role and common pathways by which the epithelial-endothelial barrier contributes to the pathogenesis of ARDS.

Preliminary therapeutic and mechanistic evaluation of S-allylmercapto-N-acetylcysteine in the treatment of pulmonary emphysema

The objective of this work was to study the effects and mechanisms of S-allylmercapto-N-acetylcysteine (ASSNAC) in the treatment of pulmonary emphysema based on network pharmacology analysis and other techniques. Firstly, the potential targets associated with ASSNAC and COPD were integrated using public databases. Then, a protein-protein interaction network was constructed using String database and Cytoscape software. The Gene Ontology analysis and Kyoto Encyclopedia of Genes and Genomes pathway analysis were performed on DAVID platform. The molecular docking of ASSNAC with some key disease targets was implemented on the SwissDock platform. To verify the results of the network pharmacology, a pulmonary emphysema mice model was established and treated with ASSNAC. Besides, the expressions of the predicted targets were detected by immunohistochemistry, Western blot analysis or enzyme-linked immunosorbent assay. Results showed that 33 overlapping targets are achieved, including CXCL8, ICAM1, MAP2K1, PTGS2, ACE and so on. The critical pathways of ASSNAC against COPD involved arachidonic acid metabolism, chemokine pathway, MAPK pathway, renin-angiotensin system, and others. Pharmacodynamic experiments demonstrated that ASSNAC decreased the pulmonary emphysema and inflammation in the pulmonary emphysema mice. Therefore, these results confirm the perspective of network pharmacology in the target verification, and indicate the treatment potential of ASSNAC against COPD.

Exploring the Mystery of Angiotensin-Converting Enzyme II (ACE2) in the Battle against SARS-CoV-2

COVID-19 is the newly born pandemic caused by the SARS-CoV-2 virus, which is the recently emerged betacoronavirus that crosses the species barrier. It predominantly infects pneumocytes of the respiratory tract, but due to the presence of angiotensin-converting enzyme II (ACE2) on other cells like surface enterocytes of the upper esophagus and colon, these are also considered as the primary sites of infection. ACE2 receptor served as a cellular entry point for SARS-CoV-2. The expression of the ACE2 receptors is regulated by several factors such as age, tobacco smoking, inflammatory signaling, ACE inhibitors, angiotensin receptor blockers, and comorbidities (chronic obstructive pulmonary disease (COPD), tuberculosis, cerebrovascular disease, coronary heart disease, hypertension, and diabetes). Therefore, scientists are trying to explore the in-depth knowledge of ACE2 and considered it as a potential indirect target for COVID-19 therapeutics. In this focused review, we discussed in detail ACE2 expressions and regulation by different factors in the primary or vulnerable sites of SARS-CoV-2 infections. Clinical trials of rhACE2 in COVID-19 patients are ongoing, and if the outcome of the trials proves positive, it will be a breakthrough for the management of COVID-19. Finally, we suggest that targeting the ACE2 (a master regulator) in a balanced way could serve as a potential option against the management of COVID-19.

The Counter Regulatory Axis of the Lung Renin-Angiotensin System in Severe COVID-19: Pathophysiology and Clinical Implications

The severe acute respiratory syndrome coronavirus (SARS-CoV)-2, which is responsible for coronavirus disease 2019 (COVID-19), uses angiotensin (ANG)-converting enzyme 2 (ACE2) as the entrance receptor. Although most COVID-19 cases are mild, some are severe or critical, predominantly due to acute lung injury. It has been widely accepted that a counter regulatory renin-angiotensin system (RAS) axis including the ACE2/ANG [1-7]/Mas protects the lungs from acute lung injury. However, recent evidence suggests that the generation of protective ANG [1-7] in the lungs is predominantly mediated by proinflammatory prolyl oligopeptidase (POP), which has been repeatedly demonstrated to be involved in lung pathology. This review contends that acute lung injury in severe COVID-19 is characterised by a) ACE2 downregulation and malfunction (inflammatory signalling) due to viral occupation, and b) dysregulation of the protective RAS axis, predominantly due to increased activity of proinflammatory POP. It follows that a reasonable treatment strategy in COVID-19-related acute lung injury would be delivering functional recombinant (r) ACE2 forms to trap the virus. Additionally, or alternatively to rACE2 delivery, the potential benefits resulting from lowering POP activity should also be explored. These treatment strategies deserve further investigation.

Male bias in ACE2 basic science research: missed opportunity for discovery in the time of COVID-19

Throughout the world, including the United States, men have worse outcomes from COVID-19 than women. SARS-CoV-2, the causative virus of the COVID-19 pandemic, uses angiotensin-converting enzyme 2 (ACE2) to gain cellular entry. ACE2 is a member of the renin-angiotensin system (RAS) and plays an important role in counteracting the harmful effects mediated by the angiotensin type 1 receptor. Therefore, we conducted Ovid MEDLINE and Embase database searches of basic science studies investigating the impact of the biological variable of sex on ACE2 expression and regulation from 2000, the year ACE2 was discovered, through December 31, 2020. Out of 2,131 publications, we identified 853 original research articles on ACE2 conducted in primary cells, tissues, and/or whole mammals excluding humans. The majority (68.7%) of these studies that cited the sex of the animal were conducted in males, while 11.2% were conducted solely in females; 9.26% compared ACE2 between the sexes, while 10.8% did not report the sex of the animals used. General findings are that sex differences are tissue-specific and when present, are dependent upon gonadal state. Renal, cardiac, and adipose ACE2 is increased in both sexes under experimental conditions that model co-morbidities associated with worse COVID-19 outcomes including hypertension, obesity, and renal and cardiovascular diseases; however, ACE2 protein was generally higher in the males. Studies in Ace2 knockout mice indicate ACE2 plays a greater role in protecting the female from developing hypertension than the male. Studying the biological variable of sex in ACE2 research provides an opportunity for discovery in conditions involving RAS dysfunction and will shed light on sex differences in COVID-19 severity.

Targeting RAGE to prevent SARS-CoV-2-mediated multiple organ failure: Hypotheses and perspectives

A novel infectious disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was detected in December 2019 and declared as a global pandemic by the World Health. Approximately 15% of patients with COVID-19 progress to severe pneumonia and eventually develop acute respiratory distress syndrome (ARDS), septic shock and/or multiple organ failure with high morbidity and mortality. Evidence points towards a determinant pathogenic role of members of the renin-angiotensin system (RAS) in mediating the susceptibility, infection, inflammatory response and parenchymal injury in lungs and other organs of COVID-19 patients. The receptor for advanced glycation end-products (RAGE), a member of the immunoglobulin superfamily, has important roles in pulmonary pathological states, including fibrosis, pneumonia and ARDS. RAGE overexpression/hyperactivation is essential to the deleterious effects of RAS in several pathological processes, including hypertension, chronic kidney and cardiovascular diseases, and diabetes, all of which are major comorbidities of SARS-CoV-2 infection. We propose RAGE as an additional molecular target in COVID-19 patients for ameliorating the multi-organ pathology induced by the virus and improving survival, also in the perspective of future infections by other coronaviruses.

Pathophysiology and pharmacological management of pulmonary and cardiovascular features of COVID-19

The first confirmed case of novel Coronavirus Disease 2019 (COVID-19) in the United States was reported on January 20, 2020. As of November 24, 2020, close to 12.2 million cases of COVID-19 was confirmed in the US, with over 255,958 deaths. The rapid transmission of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), its unusual and divergent presentation has strengthened the status of COVID-19 as a major public health threat. In this review, we aim to 1- discuss the epidemiological data from various COVID-19 patient cohorts around the world and the USA as well the associated risk factors; 2- summarize the pathophysiology of SARS-CoV-2 infection and the underlying molecular mechanisms for the respiratory and cardiovascular manifestations; 3- highlight the potential treatments and vaccines as well as current clinical trials for COVID-19.

ACE2 protein expression within isogenic cell lines is heterogeneous and associated with distinct transcriptomes

The membrane protein angiotensin-converting enzyme 2 (ACE2) is a physiologic regulator of the renin-angiotensin system and the cellular receptor for the SARS-CoV-2 virus. Prior studies of ACE2 expression have primarily focused on mRNA abundance, with investigation at the protein level limited by uncertain specificity of commercial ACE2 antibodies. Here, we report our development of a sensitive and specific flow cytometry-based assay for cellular ACE2 protein abundance. Application of this approach to multiple cell lines revealed an unexpected degree of cellular heterogeneity, with detectable ACE2 protein in only a subset of cells in each isogenic population. This heterogeneity was mediated at the mRNA level by transcripts predominantly initiated from the ACE2 proximal promoter. ACE2 expression was heritable but not fixed over multiple generations of daughter cells, with gradual drift toward the original heterogeneous background. RNA-seq profiling identified distinct transcriptomes of ACE2-expressing relative cells to non-expressing cells, with enrichment in functionally related genes and transcription factor target sets. Our findings provide a validated approach for the specific detection of ACE2 protein at the surface of single cells, support an epigenetic mechanism ACE2 gene regulation, and identify specific pathways associated with ACE2 expression in HuH7 cells.

ACE2 as therapeutic agent

The angiotensin-converting enzyme 2 (ACE2) has emerged as a critical regulator of the renin-angiotensin system (RAS), which plays important roles in cardiovascular homeostasis by regulating vascular tone, fluid and electrolyte balance. ACE2 functions as a carboxymonopeptidase hydrolyzing the cleavage of a single C-terminal residue from Angiotensin-II (Ang-II), the key peptide hormone of RAS, to form Angiotensin-(1-7) (Ang-(1-7)), which binds to the G-protein-coupled Mas receptor and activates signaling pathways that counteract the pathways activated by Ang-II. ACE2 is expressed in a variety of tissues and overwhelming evidence substantiates the beneficial effects of enhancing ACE2/Ang-(1-7)/Mas axis under many pathological conditions in these tissues in experimental models. This review will provide a succinct overview on current strategies to enhance ACE2 as therapeutic agent, and discuss limitations and future challenges. ACE2 also has other functions, such as acting as a co-factor for amino acid transport and being exploited by the severe acute respiratory syndrome coronaviruses (SARS-CoVs) as cellular entry receptor, the implications of these functions in development of ACE2-based therapeutics will also be discussed.

SARS-CoV-2 infection and smoking: What is the association? A brief review

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The link between smoking and the expression of SARS-CoV-2 key entry genes is discussed.

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Smoking-related cardiac and respiratory diseases are risk factors for COVID-19.

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The impact of smoking on ACE-2 and TMPRSS2 receptors expression is controversial.

Susceptibility to severe illness from COVID-19 is anticipated to be associated with cigarette smoking as it aggravates the risk of cardiovascular and respiratory illness, including infections. This is particularly important with the advent of a new strain of coronaviruses, the severe acute respiratory syndrome coronavirus (SARS-CoV-2) that has led to the present pandemic, coronavirus disease 2019 (COVID-19). Although, the effects of smoking on COVID-19 are less described and controversial, we presume a link between smoking and COVID-19. Smoking has been shown to enhance the expression of the angiotensin-converting enzyme-2 (ACE-2) and transmembrane serine protease 2 (TMPRSS2) key entry genes utilized by SARS-CoV-2 to infect cells and induce a ‘cytokine storm’, which further increases the severity of COVID-19 clinical course. Nevertheless, the impact of smoking on ACE-2 and TMPRSS2 receptors expression remains paradoxical. Thus, further research is necessary to unravel the association between smoking and COVID-19 and to pursue the development of potential novel therapies that are able to constrain the morbidity and mortality provoked by this infectious disease. Herein we present a brief overview of the current knowledge on the correlation between smoking and the expression of SARS-CoV-2 key entry genes, clinical manifestations, and disease progression.

Downregulation of Membrane-bound Angiotensin Converting Enzyme 2 (ACE2) Receptor has a Pivotal Role in COVID-19 Immunopathology

BACKGROUND

The Coronavirus Disease 2019 (COVID-19) is becoming the major health issue in recent human history with thousands of deaths and millions of cases worldwide. Newer research and old experience with other coronaviruses highlighted a probable underlying mechanism of disturbance of the renin-angiotensin system (RAS) that is associated with the intrinsic effects of SARS-CoV-2 infection.

OBJECTIVE

In this review, we aimed to describe the intimate connections between the RAS components, the immune system and COVID-19 pathophysiology.

METHODS

This non-systematic review article summarizes recent evidence on the relationship between COVID-19 and the RAS.

RESULTS

Several studies have indicated that the downregulation of membrane-bound ACE2 may exert a key role for the impairment of immune functions and for COVID-19 patients' outcomes. The downregulation may occur by distinct mechanisms, particularly: (1) the shedding process induced by the SARS-CoV-2 fusion pathway, which reduces the amount of membrane-bound ACE2, stimulating more shedding by the high levels of Angiotensin II; (2) the endocytosis of ACE2 receptor with the virus itself and (3) by the interferon inhibition caused by SARS-CoV-2 effects on the immune system, which leads to a reduction of ACE2 receptor expression.

CONCLUSION

Recent research provides evidence of a reduction of the components of the alternative RAS axis, including ACE2 and Angiotensin-(1-7). In contrast, increased levels of Angiotensin II can activate the AT1 receptor in several organs. Consequently, increased inflammation, thrombosis and angiogenesis occur in patients infected with SARS-COV-2. Attention should be paid to the interactions of the RAS and COVID-19, mainly in the context of novel vaccines and proposed medications.

Effects of Angiotensin-Converting Enzyme Inhibitors and Angiotensin Receptor Blockers on Angiotensin-Converting Enzyme 2 Levels: A Comprehensive Analysis Based on Animal Studies

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the pathogen of coronavirus disease 2019 (COVID-19), caused the outbreak escalated to pandemic. Reports suggested that near 1-3% of COVID-19 cases have a fatal outcome. Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) are widely used in hypertension, heart failure and chronic kidney disease. These drugs have been reported to upregulate angiotensin converting enzyme 2 (ACE2) which produces Ang (1-7), the main counter-regulatory mediator of angiotensin II. This enzyme is also known as the receptor of SARS-CoV-2 promoting the cellular uptake of the virus in the airways, however, ACE2 itself proved to be protective in several experimental models of lung injury. The present study aimed to systematically review the relationship between ACEI/ARB administration and ACE2 expression in experimental models. After a comprehensive search and selection, 27 animal studies investigating ACE2 expression in the context of ACEI and ARB were identified. The majority of these papers reported increased ACE2 levels in response to ACEI/ARB treatment. This result should be interpreted in the light of the dual role of ACE2 being a promoter of viral entry to cells and a protective factor against oxidative damage in the lungs.

Angiotensin-converting enzyme 2 and kidney diseases in the era of coronavirus disease 2019

In the decades since the discovery of angiotensin-converting enzyme 2 (ACE2), its protective role in terms of antagonizing activation of the classical renin-angiotensin system (RAS) axis has been recognized in clinical and experimental studies on kidney and cardiovascular diseases. The effects of ACE inhibitor/angiotensin type 1 receptor blockers (ACEi/ARBs) on ACE2-angiotensin-(1-7) (Ang- (1-7))-Mas receptor (MasR) axis activation has encouraged the use of such blockers in patients with kidney and cardiovascular diseases, until the emergence of coronavirus disease 2019 (COVID-19). The previously unchallenged functions of the ACE2-Ang-(1-7)-MasR axis and ACEi/ARBs are being re-evaluated in the era of COVID-19; the hypothesis is that ACEi/ARBs may increase the risk of severe acute respiratory syndrome coronavirus 2 infection by upregulating the human ACE2 receptor expression level. In this review, we examine ACE2 molecular structure, function (as an enzyme of the RAS), and distribution. We explore the roles played by ACE2 in kidney, cardiovascular, and pulmonary diseases, highlighting studies that defined the benefits imparted when ACEi/ARBs activated the local ACE2- Ang-(1-7)-MasR axis. Finally, the question of whether ACEi/ARBs therapies should be stopped in COVID-19-infected patients will be reviewed by reference to the available evidence.

Opportunities, Challenges and Pitfalls of Using Cannabidiol as an Adjuvant Drug in COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection may lead to coronavirus disease 2019 (COVID-19) which, in turn, may be associated with multiple organ dysfunction. In this review, we present advantages and disadvantages of cannabidiol (CBD), a non-intoxicating phytocannabinoid from the cannabis plant, as a potential agent for the treatment of COVID-19. CBD has been shown to downregulate proteins responsible for viral entry and to inhibit SARS-CoV-2 replication. Preclinical studies have demonstrated its effectiveness against diseases of the respiratory system as well as its cardioprotective, nephroprotective, hepatoprotective, neuroprotective and anti-convulsant properties, that is, effects that may be beneficial for COVID-19. Only the latter two properties have been demonstrated in clinical studies, which also revealed anxiolytic and antinociceptive effects of CBD (given alone or together with Δ9-tetrahydrocannabinol), which may be important for an adjuvant treatment to improve the quality of life in patients with COVID-19 and to limit post-traumatic stress symptoms. However, one should be aware of side effects of CBD (which are rarely serious), drug interactions (also extending to drugs acting against COVID-19) and the proper route of its administration (vaping may be dangerous). Clearly, further clinical studies are necessary to prove the suitability of CBD for the treatment of COVID-19.

Cognitive impact of COVID-19: looking beyond the short term

COVID-19 is primarily a respiratory disease but up to two thirds of hospitalised patients show evidence of central nervous system (CNS) damage, predominantly ischaemic, in some cases haemorrhagic and occasionally encephalitic. It is unclear how much of the ischaemic damage is mediated by direct or inflammatory effects of virus on the CNS vasculature and how much is secondary to extracranial cardiorespiratory disease. Limited data suggest that the causative SARS-CoV-2 virus may enter the CNS via the nasal mucosa and olfactory fibres, or by haematogenous spread, and is capable of infecting endothelial cells, pericytes and probably neurons. Extracranially, SARS-CoV-2 targets endothelial cells and pericytes, causing endothelial cell dysfunction, vascular leakage and immune activation, sometimes leading to disseminated intravascular coagulation. It remains to be confirmed whether endothelial cells and pericytes in the cerebral vasculature are similarly targeted. Several aspects of COVID-19 are likely to impact on cognition. Cerebral white matter is particularly vulnerable to ischaemic damage in COVID-19 and is also critically important for cognitive function. There is accumulating evidence that cerebral hypoperfusion accelerates amyloid-β (Aβ) accumulation and is linked to tau and TDP-43 pathology, and by inducing phosphorylation of α-synuclein at serine-129, ischaemia may also increase the risk of development of Lewy body disease. Current therapies for COVID-19 are understandably focused on supporting respiratory function, preventing thrombosis and reducing immune activation. Since angiotensin-converting enzyme (ACE)-2 is a receptor for SARS-CoV-2, and ACE inhibitors and angiotensin receptor blockers are predicted to increase ACE-2 expression, it was initially feared that their use might exacerbate COVID-19. Recent meta-analyses have instead suggested that these medications are protective. This is perhaps because SARS-CoV-2 entry may deplete ACE-2, tipping the balance towards angiotensin II-ACE-1-mediated classical RAS activation: exacerbating hypoperfusion and promoting inflammation. It may be relevant that APOE ε4 individuals, who seem to be at increased risk of COVID-19, also have lowest ACE-2 activity. COVID-19 is likely to leave an unexpected legacy of long-term neurological complications in a significant number of survivors. Cognitive follow-up of COVID-19 patients will be important, especially in patients who develop cerebrovascular and neurological complications during the acute illness.

Endothelial Damage in Acute Respiratory Distress Syndrome

The pulmonary endothelium is a metabolically active continuous monolayer of squamous endothelial cells that internally lines blood vessels and mediates key processes involved in lung homoeostasis. Many of these processes are disrupted in acute respiratory distress syndrome (ARDS), which is marked among others by diffuse endothelial injury, intense activation of the coagulation system and increased capillary permeability. Most commonly occurring in the setting of sepsis, ARDS is a devastating illness, associated with increased morbidity and mortality and no effective pharmacological treatment. Endothelial cell damage has an important role in the pathogenesis of ARDS and several biomarkers of endothelial damage have been tested in determining prognosis. By further understanding the endothelial pathobiology, development of endothelial-specific therapeutics might arise. In this review, we will discuss the underlying pathology of endothelial dysfunction leading to ARDS and emerging therapies. Furthermore, we will present a brief overview demonstrating that endotheliopathy is an important feature of hospitalised patients with coronavirus disease-19 (COVID-19).

The Role of Hypertension and Renin-angiotensin-aldosterone System Inhibitors in Bleomycin-induced Lung Injury

INTRODUCTION

The risk factors for bleomycin-induced lung injury (BLI), a fatal complication of cancer chemotherapy, are not well-established. The renin-angiotensin-aldosterone system (RAAS) has recently been suggested to play a role in the development of lung injury. This study clarified the impact of hypertension (HTN) and the administration of RAAS inhibitors on BLI occurrence in patients treated with bleomycin-containing regimens.

PATIENTS AND METHODS

We retrospectively analyzed the data of 190 patients treated with a bleomycin-containing regimen for Hodgkin lymphoma or germ cell tumors at our institutions from 2004 to 2018.

RESULTS

Overall, 190 patients received bleomycin, and symptomatic BLI occurred in 21 (11.1%) cases. In the multivariate analysis, age ≥ 65 years (odd ratio, 10.90; 95% confidence interval, 3.72-32.20; P < .001) and history of HTN (odds ratio, 3.32; 95% confidence interval, 1.07-10.30; P = .04) were found to be significant risk factors for BLI onset. BLI occurred in 3.6% (n = 5) of patients with no risk, 11.8% (n = 2) of those whose only risk factor was HTN, 31.6% (n = 6) of those whose only risk factor was age ≥ 65 years, and 57.1% (n = 8) of those with both risk factors (P < .001). BLI-induced mortality rates in each group were 0.0% (n = 0), 5.9% (n = 1), 10.5% (n = 2), and 42.9% (n = 6) (P < .001), respectively. Among 31 patients with HTN, BLI incidence was 12.5% in patients who were administered RAAS inhibitors and 53.3% in those who were not (P = .02).

CONCLUSION

Older age and history of HTN were independent risk factors for the development of BLI, and the administration of RAAS inhibitors might reduce the onset of BLI.

Effect of Common Medications on the Expression of SARS-CoV-2 Entry Receptors in Kidney Tissue

Besides the respiratory system, severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection was shown to affect other essential organs such as the kidneys. Early kidney involvement during the course of infection was associated with worse outcomes, which could be attributed to the direct SARS-CoV-2 infection of kidney cells. In this study, the effect of commonly used medications on the expression of SARS-CoV-2 receptor, angiotensin-converting enzyme (ACE)2, and TMPRSS2 protein in kidney tissues was evaluated. This was done by in silico analyses of publicly available transcriptomic databases of kidney tissues of rats treated with multiple doses of commonly used medications. Of 59 tested medications, 56% modified ACE2 expression, whereas 24% modified TMPRSS2 expression. ACE2 was increased with only a few of the tested medication groups, namely the renin-angiotensin inhibitors, such as enalapril, antibacterial agents, such as nitrofurantoin, and the proton pump inhibitor, omeprazole. The majority of the other medications decreased ACE2 expression to variable degrees with allopurinol and cisplatin causing the most noticeable downregulation. The expression level of TMPRSS2 was increased with a number of medications, such as diclofenac, furosemide, and dexamethasone, whereas other medications, such as allopurinol, suppressed the expression of this gene. The prolonged exposure to combinations of these medications could regulate the expression of ACE2 and TMPRSS2 in a way that may affect kidney susceptibility to SARS-CoV-2 infection. Data presented here suggest that we should be vigilant about the potential effects of commonly used medications on kidney tissue expression of ACE2 and TMPRSS2.

Renin-Angiotensin System: An Important Player in the Pathogenesis of Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is characterized by massive inflammation, increased vascular permeability and pulmonary edema. Mortality due to ARDS remains very high and even in the case of survival, acute lung injury can lead to pulmonary fibrosis. The renin-angiotensin system (RAS) plays a significant role in these processes. The activities of RAS molecules are subject to dynamic changes in response to an injury. Initially, increased levels of angiotensin (Ang) II and des-Arg⁹-bradykinin (DABK), are necessary for an effective defense. Later, augmented angiotensin converting enzyme (ACE) 2 activity supposedly helps to attenuate inflammation. Appropriate ACE2 activity might be decisive in preventing immune-induced damage and ensuring tissue repair. ACE2 has been identified as a common target for different pathogens. Some Coronaviruses, including SARS-CoV-2, also use ACE2 to infiltrate the cells. A number of questions remain unresolved. The importance of ACE2 shedding, associated with the release of soluble ACE2 and ADAM17-mediated activation of tumor necrosis factor-α (TNF-α)-signaling is unclear. The roles of other non-classical RAS-associated molecules, e.g., alamandine, Ang A or Ang 1-9, also deserve attention. In addition, the impact of established RAS-inhibiting drugs on the pulmonary RAS is to be elucidated. The unfavorable prognosis of ARDS and the lack of effective treatment urge the search for novel therapeutic strategies. In the context of the ongoing SARS-CoV-2 pandemic and considering the involvement of humoral disbalance in the pathogenesis of ARDS, targeting the renin-angiotensin system and reducing the pathogen's cell entry could be a promising therapeutic strategy in the struggle against COVID-19.

ACE2 mouse models: a toolbox for cardiovascular and pulmonary research

Angiotensin-converting enzyme 2 (ACE2) has been identified as the host entry receptor for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) responsible for the COVID-19 pandemic. ACE2 is a regulatory enzyme of the renin-angiotensin system and has protective functions in many cardiovascular, pulmonary and metabolic diseases. This review summarizes available murine models with systemic or organ-specific deletion of ACE2, or with overexpression of murine or human ACE2. The purpose of this review is to provide researchers with the genetic tools available for further understanding of ACE2 biology and for the investigation of ACE2 in the pathogenesis and treatment of COVID-19.

Implications of COVID-19 Pandemic on Evolution of Diabetes in Malaria-Endemic African Region

The coronavirus disease 2019 (COVID-19) pandemic continues to cause havoc to many countries of the globe, with no end in sight, due to nonavailability of a given vaccine or treatment regimen. The pandemic has so far had a relatively limited impact on the African continent, which contributes more than 93% of global malaria burden. However, the limited burden of COVID-19 pandemic on the African region could have long-term implications on the health and wellbeing of affected inhabitants due to its malaria-endemic status. Malaria causes recurrent insulin resistance with episodes of infection at relatively low parasitaemia. Angiotensin-converting enzyme 2 (ACE2) which is widely distributed in the human body is implicated in the pathogenesis of malaria, type 2 diabetes mellitus (T2DM), and COVID-19. Use of ACE2 by the COVID-19 virus induces inflammation and oxidative stress, which can lead to insulin resistance. Although COVID-19 patients in malaria-endemic African region may not exhibit severe signs and symptoms of the disease, their risk of exhibiting heightened insulin resistance and possible future development of T2DM is high due to their prior exposure to malaria. African governments must double efforts at containing the continued spread of the virus without neglecting existing malarial control measures if the region is to avert the plausible long-term impact of the pandemic in terms of future development of T2DM.

Renin-angiotensin-system inhibition in the context of corona virus disease-19: experimental evidence, observational studies, and clinical implications

Coronavirus disease 2019 (COVID-19) is due to severe acute respiratory syndrome coronavirus (SARS-CoV)-2 which binds and enters the host cells through the angiotensin-converting enzyme (ACE)2. While the potential for benefit with the use of renin-angiotensin-aldosterone system inhibitors (RAASi) and the risks from stopping them is more evident, potential harm by RAΑSi may also be caused by the increase in the activity of the ACE2 receptor, the inefficient counter regulatory axis in the lungs in which the proinflammatory prolyloligopeptidase (POP) is the main enzyme responsible for the conversion of deleterious angiotensin (ANG) II to protective ANG [1-7] and the proinflammatory properties of ACE2(+) cells infected with SARS-CoV-2. Acknowledging the proven RAΑSi benefit in patients with several diseases such as hypertension, heart failure, coronary disease, and diabetic kidney disease in the non-COVID-19 era, it is a reasonable strategy in this period of uncertainty to use these agents judiciously with careful consideration and to avoid the use of RAASi in select patients whenever possible, until definitive evidence becomes available.

ACE2 (Angiotensin-Converting Enzyme 2) in Cardiopulmonary Diseases: Ramifications for the Control of SARS-CoV-2

Discovery of ACE2 (angiotensin-converting enzyme 2) revealed that the renin-angiotensin system has 2 counterbalancing arms. ACE2 is a major player in the protective arm, highly expressed in lungs and gut with the ability to mitigate cardiopulmonary diseases such as inflammatory lung disease. ACE2 also exhibits activities involving gut microbiome, nutrition, and as a chaperone stabilizing the neutral amino acid transporter, B⁰AT1, in gut. But the current interest in ACE2 arises because it is the cell surface receptor for the novel coronavirus, severe acute respiratory syndrome coronavirus-2, to infect host cells, similar to severe acute respiratory syndrome coronavirus-2. This suggests that ACE2 be considered harmful, however, because of its important other roles, it is paradoxically a potential therapeutic target for cardiopulmonary diseases, including coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus-2. This review describes the discovery of ACE2, its physiological functions, and its place in the renin-angiotensin system. It illustrates new analyses of the structure of ACE2 that provides better understanding of its actions particularly in lung and gut, shedding of ACE2 by ADAM17 (a disintegrin and metallopeptidase domain 17 protein), and role of TMPRSS2 (transmembrane serine proteases 2) in severe acute respiratory syndrome coronavirus-2 entry into host cells. Cardiopulmonary diseases are associated with decreased ACE2 activity and the mitigation by increasing ACE2 activity along with its therapeutic relevance are addressed. Finally, the potential use of ACE2 as a treatment target in COVID-19, despite its role to allow viral entry into host cells, is suggested.

SARS-CoV-2 Infection and Lung Cancer: Potential Therapeutic Modalities

Human coronaviruses, especially SARS-CoV-2, are emerging pandemic infectious diseases with high morbidity and mortality in certain group of patients. In general, SARS-CoV-2 causes symptoms ranging from the common cold to severe conditions accompanied by lung injury, acute respiratory distress syndrome in addition to other organs' destruction. The main impact upon SARS-CoV-2 infection is damage to alveolar and acute respiratory failure. Thus, lung cancer patients are identified as a particularly high-risk group for SARS-CoV-2 infection and its complications. On the other hand, it has been reported that SARS-CoV-2 spike (S) protein binds to angiotensin-converting enzyme 2 (ACE-2), that promotes cellular entry of this virus in concert with host proteases, principally transmembrane serine protease 2 (TMPRSS2). Today, there are no vaccines and/or effective drugs against the SARS-CoV-2 coronavirus. Thus, manipulation of key entry genes of this virus especially in lung cancer patients could be one of the best approaches to manage SARS-CoV-2 infection in this group of patients. We herein provide a comprehensive and up-to-date overview of the role of ACE-2 and TMPRSS2 genes, as key entry elements as well as therapeutic targets for SARS-CoV-2 infection, which can help to better understand the applications and capacities of various remedial approaches for infected individuals, especially those with lung cancer.

Cigarette Smoke Exposure and Inflammatory Signaling Increase the Expression of the SARS-CoV-2 Receptor ACE2 in the Respiratory Tract

The factors mediating fatal SARS-CoV-2 infections are poorly understood. Here, we show that cigarette smoke causes a dose-dependent upregulation of angiotensin converting enzyme 2 (ACE2), the SARS-CoV-2 receptor, in rodent and human lungs. Using single-cell sequencing data, we demonstrate that ACE2 is expressed in a subset of secretory cells in the respiratory tract. Chronic smoke exposure triggers the expansion of this cell population and a concomitant increase in ACE2 expression. In contrast, quitting smoking decreases the abundance of these secretory cells and reduces ACE2 levels. Finally, we demonstrate that ACE2 expression is responsive to inflammatory signaling and can be upregulated by viral infections or interferon treatment. Taken together, these results may partially explain why smokers are particularly susceptible to severe SARS-CoV-2 infections. Furthermore, our work identifies ACE2 as an interferon-stimulated gene in lung cells, suggesting that SARS-CoV-2 infections could create positive feedback loops that increase ACE2 levels and facilitate viral dissemination.

ACE2, Much More Than Just a Receptor for SARS-COV-2

The rapidly evolving pandemic of severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection worldwide cost many lives. The angiotensin converting enzyme-2 (ACE-2) has been identified as the receptor for the SARS-CoV-2 viral entry. As such, it is now receiving renewed attention as a potential target for anti-viral therapeutics. We review the physiological functions of ACE2 in the cardiovascular system and the lungs, and how the activation of ACE2/MAS/G protein coupled receptor contributes in reducing acute injury and inhibiting fibrogenesis of the lungs and protecting the cardiovascular system. In this perspective, we predominantly focus on the impact of SARS-CoV-2 infection on ACE2 and dysregulation of the protective effect of ACE2/MAS/G protein pathway vs. the deleterious effect of Renin/Angiotensin/Aldosterone. We discuss the potential effect of invasion of SARS-CoV-2 on the function of ACE2 and the loss of the protective effect of the ACE2/MAS pathway in alveolar epithelial cells and how this may amplify systemic deleterious effect of renin-angiotensin aldosterone system (RAS) in the host. Furthermore, we speculate the potential of exploiting the modulation of ACE2/MAS pathway as a natural protection of lung injury by modulation of ACE2/MAS axis or by developing targeted drugs to inhibit proteases required for viral entry.