The ACE2-deficient mouse: A model for a cytokine storm-driven inflammation

Dry eye disease caused by viral infection: Past, present and future

Following viral infection, the innate immune system senses viral products, such as viral nucleic acids, to activate innate defence pathways, leading to inflammation and apoptosis, control of cell proliferation, and consequently, threat to the whole body. The ocular surface is exposed to the external environment and extremely vulnerable to viral infection. Several studies have revealed that viral infection can induce inflammation of the ocular surface and reduce tear secretion of the lacrimal gland (LG), consequently triggering ocular morphological and functional changes and resulting in dry eye disease (DED). Understanding the mechanisms of DED caused by viral infection and its potential therapeutic strategies are crucial for clinical interventional advances in DED. This review summarizes the roles of viral infection in the pathogenesis of DED, applicable diagnostic and therapeutic strategies, and potential regions of future studies.

Emergence of SARS-CoV-2 Variants Are Induced by Coinfections With Dengue

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that emerged in late 2019 has accumulated a series of point mutations and evolved into several variants of concern (VOCs), some of which are more transmissible and potentially more severe than the original strain. The most notable VOCs are Alpha, Beta, Gamma, Delta, and Omicron, which have spread to various parts of the world. This study conducted surveillance in Jashore, Bangladesh to identify the prevalence of SARS-CoV-2 coinfected with dengue virus and their genomic effect on the emergence of VOCs. A hospital-based COVID-19 surveillance from June to August, 2021 identified 9 453 positive patients in the surveillance area. The study enrolled 572 randomly selected COVID-19-positive patients, of which 11 (2%) had dengue viral coinfection. Whole genome sequences of SARS-CoV-2 were analyzed and compared between coinfection positive and negative group. In addition, we extracted 185 genome sequences from GISAID to investigate the cross-correlation function between SARS-CoV-2 mutations and VOC; multiple ARIMAX(p,d,q) models were developed to estimate the average number of amino acid (aa) substitution among different SARS-CoV-2 VOCs. The results of the study showed that the coinfection group had an average of 30.6 (±1.7) aa substitutions in SARS-CoV-2, whereas the dengue-negative COVID-19 group had that average of 25.6 (±1.8; P < .01). The coinfection group showed a significant difference of aa substitutions in open reading frame (ORF) and N-protein when compared to dengue-negative group (P = .03). Our ARIMAX models estimated that the emergence of SARS-CoV-2 variants Delta required additional 9 to 12 aa substitutions than Alpha, Beta, or Gamma variant. The emergence of Omicron accumulated additional 19 (95% confidence interval [CI]: 15.74, 21.95) aa substitution than Delta. Increased number of point mutations in SARS-CoV-2 genome identified from coinfected cases could be due to the compromised immune function of host and induced adaptability of pathogens during coinfections. As a result, new variants might be emerged when series of coinfection events occur during concurrent two epidemics.

Activation of limbal epithelial proliferation is partly controlled by the ACE2-LCN2 pathway

In response to corneal injury, an activation of corneal epithelial stem cells and their direct progeny the early transit amplifying (eTA) cells to rapidly proliferate is critical for proper re-epithelialization. Thus, it is important to understand how such stem/eTA cell activation is regulated. Angiotensin-converting enzyme 2 (ACE2) is predominantly expressed in the stem/eTA-enriched limbal epithelium but its role in the limbal epithelium was unclear. Single cell RNA sequencing (scRNA-seq) suggested that Ace2 involved the proliferation of the stem/eTA cells. Ace2 was reduced following corneal injury. Such reduction enhanced limbal epithelial proliferation and downregulated LCN2, a negative regulator of proliferation in a variety of tissues, via upregulating TGFA and consequently activating epidermal growth factor receptor (EGFR). Inhibition of EGFR or overexpression of LCN2 reversed the increased proliferation in limbal epithelial cells lacking ACE2. Our findings demonstrate that after corneal injury, ACE2 is downregulated, which activates limbal epithelial cell proliferation via a TGFA/EGFR/LCN2 pathway.

COVID-19-Associated Sepsis: Potential Role of Phytochemicals as Functional Foods and Nutraceuticals

The acute manifestations of coronavirus disease 2019 (COVID-19) exhibit the hallmarks of sepsis-associated complications that reflect multiple organ failure. The inflammatory cytokine storm accompanied by an imbalance in the pro-inflammatory and anti-inflammatory host response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection leads to severe and critical septic shock. The sepsis signature in severely afflicted COVID-19 patients includes cellular reprogramming and organ dysfunction that leads to high mortality rates, emphasizing the importance of improved clinical care and advanced therapeutic interventions for sepsis associated with COVID-19. Phytochemicals of functional foods and nutraceutical importance have an incredible impact on the healthcare system, which includes the prevention and/or treatment of chronic diseases. Hence, in the present review, we aim to explore the pathogenesis of sepsis associated with COVID-19 that disrupts the physiological homeostasis of the body, resulting in severe organ damage. Furthermore, we have summarized the diverse pharmacological properties of some potent phytochemicals, which can be used as functional foods as well as nutraceuticals against sepsis-associated complications of SARS-CoV-2 infection. The phytochemicals explored in this article include quercetin, curcumin, luteolin, apigenin, resveratrol, and naringenin, which are the major phytoconstituents of our daily food intake. We have compiled the findings from various studies, including clinical trials in humans, to explore more into the therapeutic potential of each phytochemical against sepsis and COVID-19, which highlights their possible importance in sepsis-associated COVID-19 pathogenesis. We conclude that our review will open a new research avenue for exploring phytochemical-derived therapeutic agents for preventing or treating the life-threatening complications of sepsis associated with COVID-19.

Fine particulate matter manipulates immune response to exacerbate microbial pathogenesis in the respiratory tract

Particulate matter with a diameter ≤2.5 μm (PM2.5) poses a substantial global challenge, with a growing recognition of pathogens contributing to diseases associated with exposure to PM2.5 Recent studies have focused on PM2.5, which impairs the immune cells in response to microbial infections and potentially contributes to the development of severe diseases in the respiratory tract. Accordingly, changes in the respiratory immune function and microecology mediated by PM2.5 are important factors that enhance the risk of microbial pathogenesis. These factors have garnered significant interest. In this review, we summarise recent studies on the potential mechanisms involved in PM2.5-mediated immune system disruption and exacerbation of microbial pathogenesis in the respiratory tract. We also discuss crucial areas for future research to address the gaps in our understanding and develop effective strategies to combat the adverse health effects of PM2.5.

Autoantibodies to ACE2 and immune molecules are associated with COVID-19 disease severity

BACKGROUND

Increased inflammation caused by SARS-CoV-2 infection can lead to severe coronavirus disease 2019 (COVID-19) and long-term disease manifestations. The mechanisms of this variable long-term immune activation are poorly defined. One feature of this increased inflammation is elevated levels of proinflammatory cytokines and chemokines. Autoantibodies targeting immune factors such as cytokines, as well as the viral host cell receptor, angiotensin-converting enzyme 2 (ACE2), have been observed after SARS-CoV-2 infection. Autoantibodies to immune factors and ACE2 could interfere with normal immune regulation and lead to increased inflammation, severe COVID-19, and long-term complications.

METHODS

Here, we deeply profiled the features of ACE2, cytokine, and chemokine autoantibodies in samples from patients recovering from severe COVID-19. We measured the levels of immunoglobulin subclasses (IgG, IgA, IgM) in the peripheral blood against ACE2 and 23 cytokines and other immune molecules. We then utilized an ACE2 peptide microarray to map the linear epitopes targeted by ACE2 autoantibodies.

RESULTS

We demonstrate that ACE2 autoantibody levels are increased in individuals with severe COVID-19 compared with those with mild infection or no prior infection. We identify epitopes near the catalytic domain of ACE2 targeted by these antibodies. Levels of autoantibodies targeting ACE2 and other immune factors could serve as determinants of COVID-19 disease severity, and represent a natural immunoregulatory mechanism in response to viral infection.

CONCLUSIONS

These results demonstrate that SARS-CoV-2 infection can increase autoantibody levels to ACE2 and other immune factors. The levels of these autoantibodies are associated with COVID-19 disease severity.

The immunobiology of SARS-CoV-2 infection and vaccine responses: potential influences of cross-reactive memory responses and aging on efficacy and off-target effects

Immune responses to both SARS-CoV-2 infection and its associated vaccines have been highly variable within the general population. The increasing evidence of long-lasting symptoms after resolution of infection, called post-acute sequelae of COVID-19 (PASC) or "Long COVID," suggests that immune-mediated mechanisms are at play. Closely related endemic common human coronaviruses (hCoV) can induce pre-existing and potentially cross-reactive immunity, which can then affect primary SARS-CoV-2 infection, as well as vaccination responses. The influence of pre-existing immunity from these hCoVs, as well as responses generated from original CoV2 strains or vaccines on the development of new high-affinity responses to CoV2 antigenic viral variants, needs to be better understood given the need for continuous vaccine adaptation and application in the population. Due in part to thymic involution, normal aging is associated with reduced naïve T cell compartments and impaired primary antigen responsiveness, resulting in a reliance on the pre-existing cross-reactive memory cell pool which may be of lower affinity, restricted in diversity, or of shorter duration. These effects can also be mediated by the presence of down-regulatory anti-idiotype responses which also increase in aging. Given the tremendous heterogeneity of clinical data, utilization of preclinical models offers the greatest ability to assess immune responses under a controlled setting. These models should now involve prior antigen/viral exposure combined with incorporation of modifying factors such as age on immune responses and effects. This will also allow for mechanistic dissection and understanding of the different immune pathways involved in both SARS-CoV-2 pathogen and potential vaccine responses over time and how pre-existing memory responses, including potential anti-idiotype responses, can affect efficacy as well as potential off-target effects in different tissues as well as modeling PASC.

Myeloid ACE2 protects against septic hypotension and vascular dysfunction through Ang-(1-7)-Mas-mediated macrophage polarization

Angiotensin converting enzyme 2 (ACE2) is a new identified member of the renin-angiotensin-aldosterone system (RAAS) that cleaves angiotensin II (Ang II) to Ang (1-7), which exerts anti-inflammatory and antioxidative activities via binding with Mas receptor (MasR). However, the functional role of ACE2 in sepsis-related hypotension remains unknown. Our results indicated that sepsis significantly reduced blood pressure and led to disruption between ACE-Ang II and ACE2-Ang (1-7) balance. ACE2 knock-in mice exhibited improved sepsis-induced mortality, hypotension and vascular dysfunction, while ACE2 knockout mice exhibited the opposite effects. Bone marrow transplantation and in vitro experiments confirmed that myeloid ACE2 exerted a protective role by suppressing oxidative stress, NO production and macrophage polarization via the Ang (1-7)-MasR-NF-κB and STAT1 pathways. Thus, ACE2 on myeloid cells could protect against sepsis-mediated hypotension and vascular dysfunction, and upregulating ACE2 may represent a promising therapeutic option for septic patients with hypotension.

Effects of particulate matter exposure on the expression of the SARS-CoV-2 ACE2 receptor in ocular surface tissues and cells

Particulate matter (PM) has been reported to be one of the risk factor for COVID-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, although the ocular surface is deeply affected by both PM exposure and SARS-COV-2 infection, no studies have investigated the effects of PM exposure on the ocular route of SARS-COV-2 infection. To this end, we explored the effects of PM on the expression of SARS-COV-2-associated receptors and proteins in ocular surface. Herein, short- and long-term PM-exposed rat models were established by topically administering PM for 3 and 10 days, respectively. Immortalized human corneal epithelial cells (HCECs) and human conjunctival epithelial cells (HCjECs) were exposed to PM. ACE2, TMPRSS2, CD147, and ADAM17 expression levels were measured by western blot analysis. Our results show that short-term PM exposure had little effect on the expressions of ACE2, TMPRSS2, and CD147 in ocular surface tissues. However, long-term PM exposure decreased the ACE2 expression in conjunctival tissues and increased the CD147 expression in corneal or conjunctival tissues. PM exposure reduced the ACE2 expression by increasing the ADAM17 expression and ACE2 shedding level in HCECs and HCjECs. Our findings suggest that long-term PM exposure down-regulate the expression of the SARS-CoV-2 receptor ACE2 in conjunctival tissues through ADAM17-dependent ACE2 shedding. However, long-term PM exposure up-regulates the expression of another SARS-CoV-2 receptor CD147 in ocular surface tissues, accompanied by ocular surface damage and cytotoxicity. This study provides a new insight into uncovering potential risk factors for infection with SARS-CoV-2 via the ocular route.

Up-to-date molecular medicine strategies for management of ocular surface neovascularization

Ocular surface neovascularization and its resulting pathological changes significantly alter corneal refraction and obstruct the light path to the retina, and hence is a major cause of vision loss. Various factors such as infection, irritation, trauma, dry eye, and ocular surface surgery trigger neovascularization via angiogenesis and lymphangiogenesis dependent on VEGF-related and alternative mechanisms. Recent advances in antiangiogenic drugs, nanotechnology, gene therapy, surgical equipment and techniques, animal models, and drug delivery strategies have provided a range of novel therapeutic options for the treatment of ocular surface neovascularization. In this review article, we comprehensively discuss the etiology and mechanisms of corneal neovascularization and other types of ocular surface neovascularization, as well as emerging animal models and drug delivery strategies that facilitate its management.

Autoantibodies against Angiotensin-converting enzyme 2 and immune molecules are associated with COVID-19 disease severity

Increased inflammation caused by SARS-CoV-2 infection can lead to severe coronavirus disease 2019 (COVID-19) and long-term disease manifestations referred to as post-acute sequalae of COVID (PASC). The mechanisms of this variable long-term immune activation are poorly defined. Autoantibodies targeting immune factors such as cytokines, as well as the viral host cell receptor, angiotensin-converting enzyme 2 (ACE2), have been observed after SARS-CoV-2 infection. Autoantibodies to immune factors and ACE2 could interfere with normal immune regulation and lead to increased inflammation, severe COVID-19, and long-term complications. Here, we deeply pro led the features of ACE2, cytokine, and chemokine autoantibodies in samples from patients recovering from severe COVID-19. We identified epitopes in the catalytic domain of ACE2 targeted by these antibodies, that could inhibit ACE2 function. Levels of autoantibodies targeting ACE2 and other immune factors could serve as determinants of COVID-19 disease severity, and represent a natural immunoregulatory mechanism in response to viral infection.

Hyperinflammatory Response in COVID-19: A Systematic Review

COVID-19 is a multisystemic disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The immunopathogenic conditions of the hyperinflammatory response that cause systemic inflammation are extremely linked to its severity. This research sought to review the immunopathological elements that contribute to its progression. This is a systematic review using the PUBMED, LILACS, MEDLINE, and SCIELO databases using articles between May 2020 and July 2022 with the following search terms in conjunction with "AND": "SARS-CoV-2"; "COVID-19"; "ARDS" and "Cytokine Storm". The quality appraisal and risk of bias were assessed by the JBI checklists and the Cochrane Collaboration's RoB 2.0 and ROBINS-I tools, respectively, and the risk of bias for in vitro studies by a pre-defined standard in the literature. The search resulted in 39 articles. The main actors in this response denote SARS-CoV-2 Spike proteins, cellular proteases, leukocytes, cytokines, and proteolytic cascades. The "cytokine storm" itself brings several complications to the host through cytokines such as IL-6 and chemokines (such as CCL2), which influence tissue inflammation through apoptosis and pyroptosis. The hyperinflammatory response causes several unfavorable outcomes in patients, and systemic inflammation caused largely by the dysregulation of the immune response should be controlled for their recovery.

Ocular Symptoms Associated with COVID-19 Are Correlated with the Expression Profile of Mouse SARS-CoV-2 Binding Sites

The COVID-19 pandemic has engendered significant scientific efforts in the understanding of its infectious agent SARS-CoV-2 and of its associated symptoms. A peculiar characteristic of this virus lies in its ability to challenge our senses, as its infection can lead to anosmia and ageusia. While ocular symptoms, such as conjunctivitis, optic neuritis or dry eyes, are also reported after viral infection, they have lower frequencies and severities, and their functional development is still elusive. Here, using combined technical approaches based on histological and gene profiling methods, we characterized the expression of SARS-CoV-2 binding sites (Ace2/Tmprss2) in the mouse eye. We found that ACE2 was ectopically expressed in subtissular ocular regions, such as in the optic nerve and in the Harderian/intraorbital lacrimal glands. Moreover, we observed an important variation of Ace2/Tmprss2 expression that is not only dependent on the age and sex of the animal, but also highly heterogenous between individuals. Our results thus give new insight into the expression of SARS-CoV-2 binding sites in the mouse eye and propose an interpretation of the human ocular-associated symptoms linked to SARS-CoV-2.

Differential proinflammatory activities of Spike proteins of SARS-CoV-2 variants of concern

The coronavirus disease 2019 (COVID-19) pandemic turned the whole world upside down in a short time. One of the main challenges faced has been to understand COVID-19-associated life-threatening hyperinflammation, the so-called cytokine storm syndrome (CSS). We report here the proinflammatory role of Spike (S) proteins from different severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern in zebrafish. We found that wild-type/Wuhan variant S1 (S1WT) promoted neutrophil and macrophage recruitment, local and systemic hyperinflammation, emergency myelopoiesis, and hemorrhages. In addition, S1γ was more proinflammatory S1δ was less proinflammatory than S1WT, and, notably, S1β promoted delayed and long-lasting inflammation. Pharmacological inhibition of the canonical inflammasome alleviated S1-induced inflammation and emergency myelopoiesis. In contrast, genetic inhibition of angiotensin-converting enzyme 2 strengthened the proinflammatory activity of S1, and angiotensin (1-7) fully rescued S1-induced hyperinflammation and hemorrhages. These results shed light into the mechanisms orchestrating the COVID-19-associated CSS and the host immune response to different SARS-CoV-2 S protein variants.

The Correlation Between Immune Invasion and SARS-COV-2 Entry Protein ADAM17 in Cancer Patients by Bioinformatic Analysis

SARS-Cov-2 caused the COVID-19 pandemic worldwide. ADAM17 functions as a disintegrin and transmembrane metalloproteinase domain protein involved in the regulation of SARS-CoV-2 receptor ACE2. However, its impact on cancer patients infected with COVID-19 and its correlation with immune cell infiltration is unclear. This study compared ADAM17 expression between normal and tumor tissues based on GEPIA. The correlations between ADAM17 expression and immune cell infiltration and immunomodulators were investigated. Besides, treated drugs for targeting ADAM17 were searched in the TISDB database. We found that ADAM17 was highly conserved in many species and was mainly expressed in lung, brain, female tissues, bone marrow and lymphoid tissues. It was also highly expressed in respiratory epithelial cells of rhinitis and bronchus. ADAM17 expression in tumors was higher than that in several paired normal tissues and was negatively correlated with the prognosis of patients with malignant tumors. Interestingly, ADAM17 expression significantly correlated with immunomodulators and immune cell infiltration in normal and tumor tissues. Moreover, eight small molecules targeting ADAM17 only demonstrate therapeutic significance. These findings imply important implications for ADAM17 in cancer patients infected with COVID-19 and provide new clues for development strategy of anti-COVID-19.

Role of angiotensin-converting enzyme 2 in fine particulate matter-induced acute lung injury

Fine particulate matter (PM2.5) pollution poses significant health concerns worldwide and can cause respiratory diseases. However, how it causes health problems is still poorly understood. Angiotensin-converting enzyme (ACE)2 is a terminal carboxypeptidase implicated in the functions of renin-angiotensin system (RAS) and plays a crucial role in the control of lung inflammation. To investigate whether ACE2 functions in PM2.5-induced lung inflammation, wild-type (WT) C57BL/6J mice and ACE2 knock-out (KO) mice were intratracheally instilled with PBS or PM2.5 suspension for 3 consecutive days, respectively. The concentrations of cytokines in bronchoalveolar lavage fluid (BALF) were determined by ELISA. The expression of ACE2 and ACE and activation of inflammatory signaling pathways in lung tissues were evaluated by immunofluorescence staining and Western blotting. We found that PM2.5 exposure increased ACE2 expression. Loss of ACE2 significantly elevated the levels of total proteins, total cells, and the concentrations of MCP-1, IL-1β in BALF after PM2.5 challenge. Additionally, loss of ACE2 enhanced lung pathologies, airway resistance, and inflammatory signaling activation. Collectively, loss of ACE2 exacerbates PM2.5-induced acute lung injury 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.

Severe Acute Respiratory Syndrome Coronavirus 2 Infection in Pregnancy. A Non-systematic Review of Clinical Presentation, Potential Effects of Physiological Adaptations in Pregnancy, and Placental Vascular Alterations

In December 2019, the novel Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) rapidly spread to become a pandemic. To date, increasing evidence has described the potential negative impact of SARS-CoV-2 infection on pregnant women. Although the pathophysiology of coronavirus disease 2019 (COVID-19) is not entirely understood, there is emerging evidence that it causes a severe systemic inflammatory response associated with vascular alterations that could be of special interest considering some physiological changes in pregnancy. Additionally, these alterations may affect the physiology of the placenta and are associated with pregnancy complications and abnormal histologic findings. On the other hand, data about the vaccine against SARS-CoV-2 are limited, but the risks of administering COVID-19 vaccines during pregnancy appear to be minimal. This review summarizes the current literature on SARSCoV2 virus infection, the development of COVID-19 and its relationship with physiological changes, and angiotensin-converting enzyme 2 (ACE2) function during pregnancy. We have particularly emphasized evidence coming from Latin American countries.

COVID-19: A systematic review and update on prevention, diagnosis, and treatment

Since the rapid onset of the COVID-19 or SARS-CoV-2 pandemic in the world in 2019, extensive studies have been conducted to unveil the behavior and emission pattern of the virus in order to determine the best ways to diagnosis of virus and thereof formulate effective drugs or vaccines to combat the disease. The emergence of novel diagnostic and therapeutic techniques considering the multiplicity of reports from one side and contradictions in assessments from the other side necessitates instantaneous updates on the progress of clinical investigations. There is also growing public anxiety from time to time mutation of COVID-19, as reflected in considerable mortality and transmission, respectively, from delta and Omicron variants. We comprehensively review and summarize different aspects of prevention, diagnosis, and treatment of COVID-19. First, biological characteristics of COVID-19 were explained from diagnosis standpoint. Thereafter, the preclinical animal models of COVID-19 were discussed to frame the symptoms and clinical effects of COVID-19 from patient to patient with treatment strategies and in-silico/computational biology. Finally, the opportunities and challenges of nanoscience/nanotechnology in identification, diagnosis, and treatment of COVID-19 were discussed. This review covers almost all SARS-CoV-2-related topics extensively to deepen the understanding of the latest achievements (last updated on January 11, 2022).

Mesenchymal Stem Cells Overexpressing ACE2 Favorably Ameliorate LPS-Induced Inflammatory Injury in Mammary Epithelial Cells

Mesenchymal stem cells (MSCs) are capable of homing injury sites to exert anti-inflammatory as well as anti-damage effects and can be used as a vehicle for gene therapy. Angiotensin-converting enzyme 2 (ACE2) plays an important role in numerous inflammatory diseases, but fewer studies have been reported in animal mastitis. We hypothesized that MSCs overexpressing ACE2 is more effective in ameliorating lipopolysaccharide (LPS)-induced inflammatory injury in mammary epithelial cells compared to MSCs alone. The results showed that MSC-ACE2 inhibited the LPS induction by upregulation of TNF-α, IL-Iβ, IL-6, and iNOS mRNA expression levels in EpH4-Ev cells compared with MSCs. Furthermore, results showed that both MSC and MSC-ACE2 were significantly activated IL-10/STAT3/SOCS3 signaling pathway as well as inhibited TLR4/NF-κB and MAPK signaling pathways, but MSC-ACE2 had more significant effects. Meanwhile, MSC-ACE2 promoted the expression of proliferation-associated proteins and inhibited the expression of the apoptosis-associated proteins in EpH4-Ev cells. In addition, MSC and MSC-ACE2 reversed the LPS-induced downregulation expression levels of the tight junction proteins in mammary epithelial cells, indicating that both MSC as well as MSC-ACE2 could promote blood-milk barrier repair, and MSC-ACE2 was more effective. These results suggested that MSCs overexpressing ACE2 were more anti-inflammatory as well as anti-injurious action into LPS-induced inflammatory injury in the EpH4-Ev cells. Thus, MSCs overexpressing ACE2 is expected to serve as a potential strategy for mastitis treatment.

Renin-angiotensin system: Basic and clinical aspects-A general perspective

The renin–angiotensin system (RAS) is one of the most complex hormonal regulatory systems, involving several organs that interact to regulate multiple body functions. The study of this system initially focused on investigating its role in the regulation of both cardiovascular function and related pathologies. From this approach, pharmacological strategies were developed for the treatment of cardiovascular diseases. However, new findings in recent decades have suggested that the RAS is much more complex and comprises two subsystems, the classic RAS and an alternative RAS, with antagonistic effects that are usually in equilibrium. The classic system is involved in pathologies where inflammatory, hypertrophic and fibrotic phenomena are common and is related to the development of chronic diseases that affect various body systems. This understanding has been reinforced by the evidence that local renin–angiotensin systems exist in many tissue types and by the role of the RAS in the spread and severity of COVID-19 infection, where it was discovered that viral entry into cells of the respiratory system is accomplished through binding to angiotensin-converting enzyme 2, which is present in the alveolar epithelium and is overexpressed in patients with chronic cardiometabolic diseases. In this narrative review, preclinical and clinical aspects of the RAS are presented and topics for future research are discussed some aspects are raised that should be clarified in the future and that call for further investigation of this system.

Potential implications of angiotensin-converting enzyme 2 blockades on neuroinflammation in SARS-CoV-2 infection

BACKGROUND

Angiotensin-converting enzyme 2 (ACE2) has been reported as a portal for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Consequently, scientific strategies to combat coronavirus disease of 2019 (COVID-19) were targeted to arrest SARS-CoV-2 invasion by blocking ACE2. While blocking ACE2 appears a beneficial approach to treat COVID-19, clinical concerns have been raised primarily due to the various intrinsic roles of ACE2 in neurological functions. Selective reports indicate that angiotensin receptor blockers (ARBs) and angiotensin-converting enzyme inhibitors (ACEIs) upregulate ACE2 levels. ACE2 metabolizes angiotensin II and several peptides, including apelin-13, neurotensin, kinetensin, dynorphin, [des-Arg9] bradykinin, and [Lys-des-Arg9]-bradykinin, which may elicit neuroprotective effects. Since ARBs and ACEIs upregulate ACE2, it may be hypothesized that patients with hypertension receiving ARBs and ACEIs may have higher expression of ACE2 and thus be at a greater risk of severe disease from the SARS-CoV-2 infections. However, recent clinical reports indicate the beneficial role of ARBs/ACEIs in reducing COVID-19 severity. Together, this warrants a further study of the effects of ACE2 blockades in hypertensive patients medicated with ARBs/ACEIs, and their consequential impact on neuronal health. However, the associations between their blockade and any neuroinflammation also warrant further research.

OBJECTIVE

This review collates mechanistic insights into the dichotomous roles of ACE2 in SARS-CoV-2 invasion and neurometabolic functions and the possible impact of ACE2 blockade on neuroinflammation.

CONCLUSION

It has been concluded that ACE2 blockade imposes neuroinflammation.

Renin-angiotensin system: Basic and clinical aspects-A general perspective

The renin–angiotensin system (RAS) is one of the most complex hormonal regulatory systems, involving several organs that interact to regulate multiple body functions. The study of this system initially focused on investigating its role in the regulation of both cardiovascular function and related pathologies. From this approach, pharmacological strategies were developed for the treatment of cardiovascular diseases. However, new findings in recent decades have suggested that the RAS is much more complex and comprises two subsystems, the classic RAS and an alternative RAS, with antagonistic effects that are usually in equilibrium. The classic system is involved in pathologies where inflammatory, hypertrophic and fibrotic phenomena are common and is related to the development of chronic diseases that affect various body systems. This understanding has been reinforced by the evidence that local renin–angiotensin systems exist in many tissue types and by the role of the RAS in the spread and severity of COVID-19 infection, where it was discovered that viral entry into cells of the respiratory system is accomplished through binding to angiotensin-converting enzyme 2, which is present in the alveolar epithelium and is overexpressed in patients with chronic cardiometabolic diseases. In this narrative review, preclinical and clinical aspects of the RAS are presented and topics for future research are discussed some aspects are raised that should be clarified in the future and that call for further investigation of this system.

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.

Bilateral corneal endothelial failure following COVID-19 pneumonia

We describe a patient who developed acute bilateral corneal decompensation following COVID-19 pneumonia and prolonged intensive care unit ventilation. SARS-CoV-2 uses human ACE2 as the receptor for entry with subsequent downregulation of ACE2. ACE2 receptors are found in human ocular surface cells including cornea. Mouse models of ACE2 deficiency result in corneal haze, oedema and ocular surface inflammation due to upregulation of the inflammatory cascades. We therefore hypothesise that the cause of this patient’s corneal decompensation was viral endotheliitis due to direct infection by the SARS-CoV-2 virus.

A systematic review on the effects of Echinacea supplementation on cytokine levels: Is there a role in COVID-19?

COVID-19 is the respiratory illness caused by the novel coronavirus, SARS-CoV-2. Cytokine storm appears to be a factor in COVID-19 mortality. Echinacea species have been used historically for immune modulation. A previous rapid review suggested that Echinacea supplementation may decrease the levels of pro-inflammatory cytokines involved in cytokine storm. The objective of the present systematic review was to identify all research that has assessed changes in levels of cytokines relevant to cytokine storm in response to administration of Echinacea supplementation. The following databases were searched: Medline (Ovid), AMED (Ovid), CINAHL (EBSCO), EMBASE (Ovid). Title and abstract screening, full text screening, and data extraction were completed in duplicate using a piloted extraction template. Risk of bias assessment was completed. Qualitative analysis was used to assess for trends in cytokine level changes. The search identified 279 unique publications. After full text screening, 105 studies met criteria for inclusion including 13 human studies, 24 animal studies, and 71 in vitro or ex vivo studies. The data suggest that Echinacea supplementation may be associated with a decrease in the pro-inflammatory cytokines IL-6, IL-8, and TNF, as well as an increase in the anti-inflammatory cytokine IL-10. The risk of bias in the included studies was generally high. While there is currently no substantive research on the therapeutic effects of Echinacea in the management of either cytokine storm or COVID-19, the present evidence related to the herb's impact on cytokine levels suggests that further research may be warranted in the form of a clinical trial involving patients with COVID-19.

Myoglobin and troponin as prognostic factors in patients with COVID-19 pneumonia

BACKGROUND

The outbreak of novel coronavirus pneumonia 2019 (COVID-19) has caused millions of deaths worldwide. It is well documented that troponin predicts the prognosis of patients. Myoglobin is not only an important marker of myocardial injury, but it indicates systemic muscle damage. However, its relationship with COVID-19 was rarely reported. The present study compared the predictive value of troponin and myoglobin on the final prognosis of COVID-19 patients by analyzing the clinical characteristics and serum levels of myoglobin and troponin in severe/critical COVID-19 patients.

METHODS

We enrolled 499 consecutive eligible hospitalized patients with severe/critical COVID-19 from February 14 to March 24, 2020 at Leishenshan Hospital, Wuhan, China. Clinical characteristics and laboratory data were collected and compared between the patients who died and survived. We analyzed the receiver operating characteristic curves of myoglobin and troponin. Then, the patients were divided into myo⁺ group, myo^- group, tro⁺ group, and tro^- group, and survival curves were analyzed. The prognostic predictable values of myoglobin and troponin were further analyzed using Cox multifactorial analysis.

RESULTS

Myoglobin and troponin were significantly elevated in the death group (134.4 [interquartile range (IQR) 24.80, 605] vs 38.02 [IQR 3.87, 11.73]ng/ml, p<0.001), and troponin was also significantly elevated in the death group (0.01 [IQR 0.01, 0.01] vs 0.04 [IQR 0.02, 0.15]ng/ml, p<0.001). The ROC curves demonstrated that the area under the curve when using myoglobin to predict patient death was 0.911, with a threshold of 1.17, which was equivalent to troponin. Kaplan-Meier survival analysis revealed a significantly lower survival curve in the myo⁺ group than the myo^- group. Multifactor Cox survival analysis showed that troponin was no longer significant (HR=0.98, 95% CI 0.92-1.03, p=0.507), but elevated myoglobin was an independent predictor of death in COVID-19 patients (HR=1.001, 95% CI 1.001-1.002, p<0.001). The analysis of the Cox model for predicting patient death and plotting decision curves suggested that the single factor myoglobin model was superior to troponin, and the predictive value of the multifactor model was superior to the single-factor analyses.

CONCLUSIONS

In severe/critical COVID-19 patients, myoglobin and troponin were predictors of mortality and the probability of conversion to critical illness, and myoglobin may be superior to troponin for predictive value.

Myoglobin and troponin as prognostic factors in patients with COVID-19 pneumonia

Background

The outbreak of novel coronavirus pneumonia 2019 (COVID-19) has caused millions of deaths worldwide. It is well documented that troponin predicts the prognosis of patients. Myoglobin is not only an important marker of myocardial injury, but it indicates systemic muscle damage. However, its relationship with COVID-19 was rarely reported. The present study compared the predictive value of troponin and myoglobin on the final prognosis of COVID-19 patients by analyzing the clinical characteristics and serum levels of myoglobin and troponin in severe/critical COVID-19 patients.

Methods

We enrolled 499 consecutive eligible hospitalized patients with severe/critical COVID-19 from February 14 to March 24, 2020 at Leishenshan Hospital, Wuhan, China. Clinical characteristics and laboratory data were collected and compared between the patients who died and survived. We analyzed the receiver operating characteristic curves of myoglobin and troponin. Then, the patients were divided into myo⁺ group, myo^- group, tro⁺ group, and tro^- group, and survival curves were analyzed. The prognostic predictable values of myoglobin and troponin were further analyzed using Cox multifactorial analysis.

Results

Myoglobin and troponin were significantly elevated in the death group (134.4 [interquartile range (IQR) 24.80, 605] vs 38.02 [IQR 3.87, 11.73] ng/ml, p < 0.001), and troponin was also significantly elevated in the death group (0.01 [IQR 0.01, 0.01] vs 0.04 [IQR 0.02, 0.15] ng/ml, p < 0.001). The ROC curves demonstrated that the area under the curve when using myoglobin to predict patient death was 0.911, with a threshold of 1.17, which was equivalent to troponin. Kaplan-Meier survival analysis revealed a significantly lower survival curve in the myo⁺ group than the myo^- group. Multifactor Cox survival analysis showed that troponin was no longer significant (HR = 0.98, 95% CI 0.92-1.03, p = 0.507), but elevated myoglobin was an independent predictor of death in COVID-19 patients (HR = 1.001, 95% CI 1.001-1.002, p < 0.001). The analysis of the Cox model for predicting patient death and plotting decision curves suggested that the single factor myoglobin model was superior to troponin, and the predictive value of the multifactor model was superior to the single-factor analyses.

Conclusions

In severe/critical COVID-19 patients, myoglobin and troponin were predictors of mortality and the probability of conversion to critical illness, and myoglobin may be superior to troponin for predictive value.

Diagnostic Significance of Serum Galectin-3 in Hospitalized Patients with COVID-19-A Preliminary Study

Severe coronavirus disease 2019 (COVID-19) is associated with hyperinflammation leading to organ injury, including respiratory failure. Galectin-3 was implicated in innate immunological response to infections and in chronic fibrosis. The aim of our preliminary study was the assessment of the diagnostic utility of serum galectin-3 in patients with COVID-19. The prospective observational study included adult patients admitted with active COVID-19 and treated in tertiary hospital between June and July 2020. The diagnosis was confirmed by the quantitative detection of nucleic acid of severe acute respiratory syndrome coronavirus 2 in nasopharyngeal swabs. Galectin-3 was measured by enzyme immunoassay in serum samples obtained during the first five days of hospital stay. We included 70 patients aged 25 to 73 years; 90% had at least one comorbidity. During the hospital stay, 32.9% were diagnosed with COVID-19 pneumonia and 12.9% required treatment in the intensive care unit (ICU). Serum galectin-3 was significantly increased in patients who developed pneumonia, particularly those who required ICU admission. Positive correlations were found between galectin-3 and inflammatory markers (interleukin-6, C-reactive protein, ferritin, pentraxin-3), a marker of endothelial injury (soluble fms-like tyrosine kinase-1), and a range of tissue injury markers. Serum galectin-3 enabled the diagnosis of pneumonia with moderate diagnostic accuracy and the need for ICU treatment with high diagnostic accuracy. Our findings strengthen the hypothesis that galectin-3 may be involved in severe COVID-19. Further studies are planned to confirm the preliminary results and to verify possible associations of galectin-3 with long-term consequences of COVID-19, including pulmonary fibrosis.

The Altered Anatomical Distribution of ACE2 in the Brain With Alzheimer's Disease Pathology

The whole world is suffering from the coronavirus disease 2019 (COVID-19) pandemic, induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) through angiotensin-converting enzyme 2 (ACE2). Neurological manifestations in COVID-19 patients suggested the invasion of SARS-CoV-2 into the central nervous system. The present study mapped the expression level of ACE2 in 12 brain regions through immunohistochemistry and detected ACE2 in endothelial cells and non-vascular cells. The comparison among brain regions found that pons, visual cortex, and amygdala presented a relatively high level of ACE2. In addition, this study demonstrates that the protein level of ACE2 was downregulated in the basal nucleus, hippocampus and entorhinal cortex, middle frontal gyrus, visual cortex, and amygdala of the brain with Alzheimer’s disease (AD) pathology. Collectively, our results suggested that ACE2 was expressed discriminatorily at different human brain regions, which was downregulated in the brain with AD pathology. This may contribute to a comprehensive understanding of the neurological symptoms caused by SARS-CoV-2 and provide clues for further research on the relationship between COVID-19 and AD.

A Dual-Route Perspective of SARS-CoV-2 Infection: Lung- vs. Gut-specific Effects of ACE-2 Deficiency

SARS-CoV-2, primarily considered a respiratory virus, is increasingly recognized as having gastrointestinal aspects based on its presence in the gastrointestinal (GI) tract and feces. SARS-CoV-2 uses as a receptor angiotensin-converting enzyme 2 (ACE-2), a critical member of the renin-angiotensin-aldosterone system (RAAS) involved in the regulation of blood pressure and fluid system. In addition to the systemic endocrine functions, RAAS components are also involved in intracrine and organ-specific local functions. The angiotensin-converting enzyme 2 (ACE-2) is a key component of RAAS and a receptor for SARS-CoV-2. It is expressed in many tissues with gastrointestinal (GI) tract ACE-2 levels far exceeding those in the respiratory tract. SARS-CoV-2 binding to its receptor results in a deficiency of ACE-2 activity in endocrine, intracrine, and local lung and GI tract ACE-2. The local ACE-2 has different organ-specific functions, including hypertension-independent activities; dysregulations of these functions may contribute to multiorgan COVID-19 pathology, its severity, long-term effects, and mortality. We review supporting evidence from this standpoint. Notably, COVID-19 comorbidities involving hypertension, obesity, heart disease, kidney disease, and diabetes are associated with gastrointestinal problems and display ACE-2 deficits. While RAAS inhibitors target both endocrine and intracrine ACE-2 activity, the deficit of the local ACE-2 activity in the lungs and more so in the gut have not been targeted. Consequently, the therapeutic approach to COVID-19 should be carefully reconsidered. Ongoing clinical trials testing oral probiotic bound ACE-2 delivery are promising.

Emerging importance of ACE2 in external stratified epithelial tissues

Angiotensin converting enzyme 2 (ACE2), a component of the renin-angiotensin system (RAS), has been identified as the receptor for the SARS-CoV-2. Several RAS components including ACE2 and its substrate Ang II are present in both eye and skin, two stratified squamous epithelial tissues that isolate organisms from external environment. Our recent findings in cornea and others in both skin and eye suggest contribution of this system, and specifically of ACE2 in variety of physiological and pathological responses of these organ systems. This review will focus on the role RAS system plays in both skin and cornea, and will specifically discuss our recent findings on ACE2 in corneal epithelial inflammation, as well as potential implications of ACE2 in patients with COVID-19.

Revisiting Pleiotropic Effects of Type I Interferons: Rationale for Its Prophylactic and Therapeutic Use Against SARS-CoV-2

The pandemic distribution of SARS-CoV-2 together with its particular feature of inactivating the interferon-based endogenous response and accordingly, impairing the innate immunity, has become a challenge for the international scientific and medical community. Fortunately, recombinant interferons as therapeutic products have accumulated a long history of beneficial therapeutic results in the treatment of chronic and acute viral diseases and also in the therapy of some types of cancer. One of the first antiviral treatments during the onset of COVID-19 in China was based on the use of recombinant interferon alfa 2b, so many clinicians began to use it, not only as therapy but also as a prophylactic approach, mainly in medical personnel. At the same time, basic research on interferons provided new insights that have contributed to a much better understanding of how treatment with interferons, initially considered as antivirals, actually has a much broader pharmacological scope. In this review, we briefly describe interferons, how they are induced in the event of a viral infection, and how they elicit signaling after contact with their specific receptor on target cells. Additionally, some of the genes stimulated by type I interferons are described, as well as the way interferon-mediated signaling is torpedoed by coronaviruses and in particular by SARS-CoV-2. Angiotensin converting enzyme 2 (ACE2) gene is one of the interferon response genes. Although for many scientists this fact could result in an adverse effect of interferon treatment in COVID-19 patients, ACE2 expression contributes to the balance of the renin-angiotensin system, which is greatly affected by SARS-CoV-2 in its internalization into the cell. This manuscript also includes the relationship between type I interferons and neutrophils, NETosis, and interleukin 17. Finally, under the subtitle of "take-home messages", we discuss the rationale behind a timely treatment with interferons in the context of COVID-19 is emphasized.

Notable Developments for Vitamin D Amid the COVID-19 Pandemic, but Caution Warranted Overall: A Narrative Review

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel contagion that has infected over 113 million people worldwide. It is responsible for the coronavirus disease (COVID-19), which has cost the lives of 2.5 million people. Ergo, the global scientific community has been scrambling to repurpose or develop therapeutics to treat COVID-19. Dietary supplements and nutraceuticals are among those under consideration due to the link between nutritional status and patient outcomes. Overall, poor vitamin D status seems to be associated with an increased risk of COVID-19. Severely ill COVID-19 patients appear to be deficient or have suboptimal levels of serum 25-hydroxyvitamin D, a measure of vitamin D status. Consequently, vitamin D is now the subject of several prophylactic and therapeutic clinical trials. In this review, the general status of nutraceuticals and dietary supplements amid the pandemic is appraised, with a particular focus on vitamin D. Consumers should be aware of misinformation and unsubstantiated promises for products marketed for COVID-19 protection. However, maintaining a healthy diet and lifestyle will likely maintain health including optimum immune function that may affect patient outcomes. Those who are deficient in key nutrients such as vitamin D should consider lifestyle changes and potentially supplementation in consultation with their physician and/or registered dieticians.

Vascular Endothelial Glycocalyx Damage in COVID-19

The new coronavirus disease-2019 (COVID-19), which is spreading around the world and threatening people, is easily infecting a large number of people through airborne droplets; moreover, patients with hypertension, diabetes, obesity, and cardiovascular disease are more likely to experience severe conditions. Vascular endothelial dysfunction has been suggested as a common feature of high-risk patients prone to severe COVID-19, and measurement of vascular endothelial function may be recommended for predicting severe conditions in high-risk patients with COVID-19. However, fragmented vascular endothelial glycocalyx (VEGLX) is elevated in COVID-19 patients, suggesting that it may be useful as a prognostic indicator. Although the relationship between VEGLX and severe acute respiratory syndrome coronavirus 2 infections has not been well studied, some investigations into COVID-19 have clarified the relationship between VEGLX and the mechanism that leads to severe conditions. Clarifying the usefulness of VEGLX assessment as a predictive indicator of the development of severe complications is important as a strategy for confronting pandemics caused by new viruses with a high affinity for the vascular endothelium that may recur in the future.

The Rationale for Angiotensin Receptor Neprilysin Inhibitors in a Multi-Targeted Therapeutic Approach to COVID-19

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) disease (COVID-19) determines the angiotensin converting enzyme 2 (ACE2) down-regulation and related decrease in angiotensin II degradation. Both these events trigger “cytokine storm” leading to acute lung and cardiovascular injury. A selective therapy for COVID-19 has not yet been identified. Clinical trials with remdesivir gave discordant results. Thus, healthcare systems have focused on “multi-targeted” therapeutic strategies aiming at relieving systemic inflammation and thrombotic complications. No randomized clinical trial has demonstrated the efficacy of renin angiotensin system antagonists in reducing inflammation related to COVID-19. Dexamethasone and tocilizumab showed encouraging data, but their use needs to be further validated. The still-controversial efficacy of these treatments highlighted the importance of organ injury prevention in COVID-19. Neprilysin (NEP) might be an interesting target for this purpose. NEP expression is increased by cytokines on lung fibroblasts surface. NEP activity is elevated in acute respiratory distress syndrome and it is conceivable that it is also high in COVID-19. NEP is implicated in the degradation of natriuretic peptides, bradykinin, substance P, adrenomedullin, and apelin that account for prevention of organ injury. Thus, NEP/angiotensin receptor type 1 (AT1R) inhibitor sacubitril/valsartan (SAC/VAL) may increase levels of these molecules and block AT1Rs required for ACE2 endocytosis in SARS-CoV-2 infection. Moreover, SAC/VAL has a positive impact on acute heart failure that is very frequently observed in deceased COVID-19 patients. The current review aims to summarize actual therapeutic strategies for COVID-19 and to examine the data supporting the potential benefits of SAC/VAL in COVID-19 treatment.

Twenty years of progress in angiotensin converting enzyme 2 and its link to SARS-CoV-2 disease

The virulence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and the aggressive nature of the disease has transformed the universal pace of research in the desperate attempt to seek effective therapies to halt the morbidity and mortality of this pandemic. The rapid sequencing of the SARS-CoV-2 virus facilitated identification of the receptor for angiotensin converting enzyme 2 (ACE2) as the high affinity binding site that allows virus endocytosis. Parallel evidence that coronavirus disease 2019 (COVID-19) disease evolution shows greater lethality in patients with antecedent cardiovascular disease, diabetes, or even obesity questioned the potential unfavorable contribution of angiotensin converting enzyme (ACE) inhibitors or angiotensin II (Ang II) receptor blockers as facilitators of adverse outcomes due to the ability of these therapies to augment the transcription of Ace2 with consequent increase in protein formation and enzymatic activity. We review, here, the specific studies that support a role of these agents in altering the expression and activity of ACE2 and underscore that the robustness of the experimental data is associated with weak clinical long-term studies of the existence of a similar regulation of tissue or plasma ACE2 in human subjects.

HDL nanoparticles have wound healing and anti-inflammatory properties and can topically deliver miRNAs

microRNAs regulate numerous biological processes, making them potential therapeutic agents. Problems with delivery and stability of these molecules have limited their usefulness as treatments. We demonstrate that synthetic high-density lipoprotein nanoparticles (HDL NPs) topically applied to the intact ocular surface are taken up by epithelial and stromal cells. microRNAs complexed to HDL NPs (miR-HDL NPs) are similarly taken up by cells and tissues and retain biological activity. Topical treatment of diabetic mice with either HDL NPs or miR-HDL NPs significantly improved corneal re-epithelialization following wounding compared with controls. Mouse corneas with alkali burn-induced inflammation, topically treated with HDL NPs, displayed clinical, morphological and immunological improvement. These results should yield a novel HDL NP-based eye drop for patients with compromised wound healing ability (diabetics) and/or corneal inflammatory diseases (e.g. dry eye).

The ACE2-deficient mouse: A model for a cytokine storm-driven inflammation

Angiotensin converting enzyme 2 (ACE2) plays an important role in inflammation, which is attributable at least, in part, to the conversion of the pro-inflammatory angiotensin (Ang) II peptide into angiotensin 1-7 (Ang 1-7), a peptide which opposes the actions of AngII. ACE2 and AngII are present in many tissues but information on the cornea is lacking. We observed that mice deficient in the Ace2 gene (Ace2-/- ), developed a cloudy cornea phenotype as they aged. Haze occupied the central cornea, accompanied by corneal edema and neovascularization. In severe cases with marked chronic inflammation, a cell-fate switch from a transparent corneal epithelium to a keratinized, stratified squamous, psoriasiform-like epidermis was observed. The stroma contained a large number of CD11c, CD68, and CD3 positive cells. Corneal epithelial debridement experiments in young ACE2-deficient mice showed normal appearing corneas, devoid of haze. We hypothesized, however, that these mice are "primed" for a corneal inflammatory response, which once initiated, would persist. In vitro studies reveal that interleukins (IL-1a, IL-1b), chemokines (CCL2, CXCL8), and TNF-α, are all significantly elevated, resulting in a cytokine storm-like phenotype. This phenotype could be partially rescued by treatment with the AngII type 1 receptor (AT1R) antagonist, losartan, suggesting that the observed effect was mediated by AngII acting on its main receptor. Since the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) utilizes human ACE2 as the receptor for entry with subsequent downregulation of ACE2, corneal inflammation in Ace2-/- mice may have a similar mechanism with that in COVID-19 patients. Thus the Ace2-/- cornea, because of easy accessibility, may provide an attractive model to explore the molecular mechanisms, immunological changes, and treatment modalities in patients with COVID-19.