N-linked glycoproteins and host proteases are involved in swine acute diarrhea syndrome coronavirus entry

IMPORTANCE

Gaining insight into the cell-entry mechanisms of swine acute diarrhea syndrome coronavirus (SADS-CoV) is critical for investigating potential cross-species infections. Here, we demonstrated that pretreatment of host cells with tunicamycin decreased SADS-CoV attachment efficiency, indicating that N-linked glycosylation of host cells was involved in SADS-CoV entry. Common N-linked sugars Neu5Gc and Neu5Ac did not interact with the SADS-CoV S1 protein, suggesting that these molecules were not involved in SADS-CoV entry. Additionally, various host proteases participated in SADS-CoV entry into diverse cells with different efficiencies. Our findings suggested that SADS-CoV may exploit multiple pathways to enter cells, providing insights into intervention strategies targeting the cell entry of this virus.

Is mitochondrial bioenergetics and coenzyme Q10 the target of a virus causing COVID-19?

COVID-19 ‒ a coronavirus disease, affected almost all countries in the world. It is a new virus disease, nobody has prior immunity to it, human population is prone to infections. In March 11 2020, WHO declared the pandemic status. The main symptoms include: fever, dry cough and fatigue. Virus proteins need mitochondrial energy for their own survival and replication. Upon viral infections, mitochondrial dynamics and metabolism can be modulated, which can influence the energy production in the host cells. Coenzyme Q10 is an integral component of mitochondrial respiratory chain and the key component of mitochondrial ATP production. The exact pathobiochemical mechanism of the disease is unknown. Modulated mitochondrial dynamics and metabolism with lower CoQ10 levels in viral infections leads us to the hypothesis that one of the main pathobiochemical effects of SARS-Cov-2 virus could be mitochondrial bioenergetics dysfunction with CoQ10 deficit leading to the reduction of its endogenous biosynthesis. The mechanism might be virus induced oxidative stress causing a mutation of one or more of the nine COQ genes, resulting in primary CoQ10 deficiency. New perspective for patients with COVID-19 may be supportive targeting therapy with coenzyme Q10 to increase the energy production, immunity and decrease oxidative stress (Fig. 1, Ref. 51). Keywords: COVID-19, virus, mitochondrial bioenergetics, coenzyme Q10, oxidative stress.

Glucose-6-phosphate dehydrogenase deficiency enhances Covid-19 infection in elderly people

Our understanding of the mechanisms responsible for death of aged people from Covid-19 became one of the major concerns of these days. Glucose-6-phosphate dehydrogenase (G6PD) enhances the normal senescence and accelerates the precocious removal of chronologically young, yet biologically aged cells. Thus, its deficiency is associated with an increase in the cellular oxidative stress. Accumulating evidence showed that oxidative stress has a fundamental role in several age-related diseases. Nowadays, Covid-19 is considered a serious health problem worldwide. The host cellular environment is the key determinant of pathogen Infectivity. Most respiratory viral infections have a strong association with Glucose-6-phosphate dehydrogenase. Unfortunately, this enzyme deficiency markedly decreases with aging what is involved in increasing of the morbidity rate. The aim of this mini review was to shed more light on the role of G6PD deficiency in aged people infected with Covid-19 (Ref. 20). Keywords: GSPD, Covid-19, elderly people.

Coevolution, Dynamics and Allostery Conspire in Shaping Cooperative Binding and Signal Transmission of the SARS-CoV-2 Spike Protein with Human Angiotensin-Converting Enzyme 2

Binding to the host receptor is a critical initial step for the coronavirus SARS-CoV-2 spike protein to enter into target cells and trigger virus transmission. A detailed dynamic and energetic view of the binding mechanisms underlying virus entry is not fully understood and the consensus around the molecular origins behind binding preferences of SARS-CoV-2 for binding with the angiotensin-converting enzyme 2 (ACE2) host receptor is yet to be established. In this work, we performed a comprehensive computational investigation in which sequence analysis and modeling of coevolutionary networks are combined with atomistic molecular simulations and comparative binding free energy analysis of the SARS-CoV and SARS-CoV-2 spike protein receptor binding domains with the ACE2 host receptor. Different from other computational studies, we systematically examine the molecular and energetic determinants of the binding mechanisms between SARS-CoV-2 and ACE2 proteins through the lens of coevolution, conformational dynamics, and allosteric interactions that conspire to drive binding interactions and signal transmission. Conformational dynamics analysis revealed the important differences in mobility of the binding interfaces for the SARS-CoV-2 spike protein that are not confined to several binding hotspots, but instead are broadly distributed across many interface residues. Through coevolutionary network analysis and dynamics-based alanine scanning, we established linkages between the binding energy hotspots and potential regulators and carriers of signal communication in the virus-host receptor complexes. The results of this study detailed a binding mechanism in which the energetics of the SARS-CoV-2 association with ACE2 may be determined by cumulative changes of a number of residues distributed across the entire binding interface. The central findings of this study are consistent with structural and biochemical data and highlight drug discovery challenges of inhibiting large and adaptive protein-protein interfaces responsible for virus entry and infection transmission.

Targeting zinc metalloenzymes in coronavirus disease 2019

Several lines of evidence support a link between the essential element zinc and the coronavirus disease 2019 (COVID-19). An important fact is that zinc is present in proteins of humans and of viruses. Some zinc sites in viral enzymes may serve as drug targets and may liberate zinc ions, thus leading to changes in intracellular concentration of zinc ions, while increased intracellular zinc may induce biological effects in both the host and the virus. Drugs such as chloroquine may contribute to increased intracellular zinc. Moreover, clinical trials on the use of zinc alone or in addition to other drugs in the prophylaxis/treatment of COVID-19 are ongoing. Thereby, we aim to discuss the rationale for targeting zinc metalloenzymes as a new strategy for the treatment of COVID-19. LINKED ARTICLES: This article is part of a themed issue on The Pharmacology of COVID-19. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.21/issuetoc.

Poly(ADP-Ribose) Polymerase Inhibition in Acute Lung Injury. A Reemerging Concept

PARP1, the major isoform of a family of ADP-ribosylating enzymes, has been implicated in the regulation of various biological processes including DNA repair, gene transcription, and cell death. The concept that PARP1 becomes activated in acute lung injury (ALI) and that pharmacological inhibition or genetic deletion of this enzyme can provide therapeutic benefits emerged over 20 years ago. The current article provides an overview of the cellular mechanisms involved in the pathogenetic roles of PARP1 in ALI and provides an overview of the preclinical data supporting the efficacy of PARP (poly[ADP-ribose] polymerase) inhibitors. In recent years, several ultrapotent PARP inhibitors have been approved for clinical use (for the therapy of various oncological diseases): these newly-approved PARP inhibitors were recently reported to show efficacy in animal models of ALI. These observations offer the possibility of therapeutic repurposing of these inhibitors for patients with ALI. The current article lays out a potential roadmap for such repurposing efforts. In addition, the article also overviews the scientific basis of potentially applying PARP inhibitors for the experimental therapy of viral ALI, such as coronavirus disease (COVID-19)-associated ALI.

Endocrine aspects of ACE2 regulation: RAAS, steroid hormones and SARS-CoV-2

Coronavirus disease (COVID-19) is caused by a new strain of coronavirus, the severe acute respiratory syndrome coronavirus 2 or SARS-CoV-2. At the time of writing, SARS-CoV-2 has infected over 5 million people worldwide. A key step in understanding the pathobiology of the SARS-CoV-2 was the identification of -converting enzyme 2 (ACE2) as the receptor for SARS-CoV-2 to gain entry into host cells. ACE2 is an established component of the 'protective arm' of the renin-angiotensin-aldosterone-system (RAAS) that opposes ACE/angiotensin II (ANG II) pressor and tissue remodelling actions. Identification of ACE2 as the entry point for SARS-CoV-2 into cells quickly focused attention on the use of ACE inhibitors (ACEi), angiotensin receptor blockers (ARB) and mineralocorticoid receptor antagonists (MRA) in patients with hypertension and cardiovascular disease given that these pharmacological agents upregulate ACE2 expression in target cells. ACE2 is cleaved from the cells by metalloproteases ADAM10 and ADAM17. Steroid hormone receptors regulate multiple components of the RAAS and may contribute to the observed variation in the incidence of severe COVID-19 between men and women, and in patients with pre-existing endocrine-related disease. Moreover, glucocorticoids play a critical role in the acute and chronic management of inflammatory disease, independent of any effect on RAAS activity. Dexamethasone, a synthetic glucocorticoid, has emerged as a life-saving treatment in severe COVID-19. This review will examine the endocrine mechanisms that control ACE2 and discusses the impact of therapies targeting the RAAS, glucocorticoid and other endocrine systems for their relevance to the impact of SARS-CoV-2 infection and the treatment and recovery from COVID-19-related critical illness.

The effect of liver test abnormalities on the prognosis of COVID-19

INTRODUCTION

COVID-19 caused by the SARS-CoV-2 continues to spread rapidly across the world. In our study, we aim to investigate the relationship between the liver enzymes on admission (AST, ALT, ALP, GGT) and severity of COVID-19. We evaluated course of disease, hospital stay, liver damage and mortality.

MATERIALS AND METHODS

Our study included 614 patients who were hospitalized with the diagnosis of COVID-19 between 03.16.20 and 05.12.20. Patients with liver disease, hematological and solid organ malignancy with liver metastases were excluded, resulting in 554 patients who met our inclusion criteria. We retrospectively evaluated liver transaminase levels, AST/ALT ratio, cholestatic enzyme levels and R ratio during hospital admission and these were compared in terms of morbidity, mortality and clinical course.

RESULTS

Mean age of 554 subjects were 66.21±15.45 years, 328 (59.2%) were men. The mean values of liver enzymes on admission were AST (36.2±33.6U/L), ALT (34.01±49.34U/L), ALP (78.8±46.86U/L), GGT (46.25±60.05U/L). Mortality rate and need for intensive care unit were statistically significant in subjects that had high ALT-AST levels during their admission to the hospital (p=0.001). According to the ROC analysis AST/ALT ratio was a good marker of mortality risk (AUC=0.713: p=0.001) and expected probability of intensive care unit admission (AUC=0.636: p=0.001). R ratio, which was used to evaluate prognosis, showed a poor prognosis rate of 26.5% in the cholestatic injury group, 36.1% in the mixed pattern group and 30% in the hepato-cellular injury group (p 0.001).

CONCLUSIONS

ALT-AST elevation and AST/ALT ratio >1 was associated with more severe course and increased mortality in COVID-19.

A hypothesis for pathobiology and treatment of COVID-19: The centrality of ACE1/ACE2 imbalance

Angiotensin Converting Enzyme2 is the cell surface binding site for the coronavirus SARS-CoV-2, which causes COVID-19. We propose that an imbalance in the action of ACE1- and ACE2-derived peptides, thereby enhancing angiotensin II (Ang II) signalling is primary driver of COVID-19 pathobiology. ACE1/ACE2 imbalance occurs due to the binding of SARS-CoV-2 to ACE2, reducing ACE2-mediated conversion of Ang II to Ang peptides that counteract pathophysiological effects of ACE1-generated ANG II. This hypothesis suggests several approaches to treat COVID-19 by restoring ACE1/ACE2 balance: (a) AT receptor antagonists; (b) ACE1 inhibitors (ACEIs); (iii) agonists of receptors activated by ACE2-derived peptides (e.g. Ang (1-7), which activates MAS1); (d) recombinant human ACE2 or ACE2 peptides as decoys for the virus. Reducing ACE1/ACE2 imbalance is predicted to blunt COVID-19-associated morbidity and mortality, especially in vulnerable patients. Importantly, approved AT antagonists and ACEIs can be rapidly repurposed to test their efficacy in treating COVID-19. LINKED ARTICLES: This article is part of a themed issue on The Pharmacology of COVID-19. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.21/issuetoc.

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.

In silico drug discovery of major metabolites from spices as SARS-CoV-2 main protease inhibitors

Coronavirus Disease 2019 (COVID-19) is an infectious illness caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), originally identified in Wuhan, China (December 2019) and has since expanded into a pandemic. Here, we investigate metabolites present in several common spices as possible inhibitors of COVID-19. Specifically, 32 compounds isolated from 14 cooking seasonings were examined as inhibitors for SARS-CoV-2 main protease (M^pro), which is required for viral multiplication. Using a drug discovery approach to identify possible antiviral leads, in silico molecular docking studies were performed. Docking calculations revealed a high potency of salvianolic acid A and curcumin as M^pro inhibitors with binding energies of -9.7 and -9.2 kcal/mol, respectively. Binding mode analysis demonstrated the ability of salvianolic acid A and curcumin to form nine and six hydrogen bonds, respectively with amino acids proximal to M^pro's active site. Stabilities and binding affinities of the two identified natural spices were calculated over 40 ns molecular dynamics simulations and compared to an antiviral protease inhibitor (lopinavir). Molecular mechanics-generalized Born surface area energy calculations revealed greater salvianolic acid A affinity for the enzyme over curcumin and lopinavir with energies of -44.8, -34.2 and -34.8 kcal/mol, respectively. Using a STRING database, protein-protein interactions were identified for salvianolic acid A included the biochemical signaling genes ACE, MAPK14 and ESR1; and for curcumin, EGFR and TNF. This study establishes salvianolic acid A as an in silico natural product inhibitor against the SARS-CoV-2 main protease and provides a promising inhibitor lead for in vitro enzyme testing.

Virus-Receptor Interactions of Glycosylated SARS-CoV-2 Spike and Human ACE2 Receptor

The SARS-CoV-2 betacoronavirus uses its highly glycosylated trimeric Spike protein to bind to the cell surface receptor angiotensin converting enzyme 2 (ACE2) glycoprotein and facilitate host cell entry. We utilized glycomics-informed glycoproteomics to characterize site-specific microheterogeneity of glycosylation for a recombinant trimer Spike mimetic immunogen and for a soluble version of human ACE2. We combined this information with bioinformatics analyses of natural variants and with existing 3D structures of both glycoproteins to generate molecular dynamics simulations of each glycoprotein both alone and interacting with one another. Our results highlight roles for glycans in sterically masking polypeptide epitopes and directly modulating Spike-ACE2 interactions. Furthermore, our results illustrate the impact of viral evolution and divergence on Spike glycosylation, as well as the influence of natural variants on ACE2 receptor glycosylation. Taken together, these data can facilitate immunogen design to achieve antibody neutralization and inform therapeutic strategies to inhibit viral infection.

Can elevated concentrations of ALT and AST predict the risk of 'recurrence' of COVID-19?

'Recurrence' of coronavirus disease 2019 (COVID-19) has triggered numerous discussions of scholars at home and abroad. A total of 44 recurrent cases of COVID-19 and 32 control cases admitted from 11 February to 29 March 2020 to Guanggu Campus of Tongji Hospital affiliated to Tongji Medical College Huazhong University of Science and Technology were enrolled in this study. All the 44 recurrent cases were classified as mild to moderate when the patients were admitted for the second time. The gender and mean age in both cases (recurrent and control) were similar. At least one concomitant disease was observed in 52.27% recurrent cases and 34.38% control cases. The most prevalent comorbidity among them was hypertension. Fever and cough being the most prevalent clinical symptoms in both cases. On comparing both the cases, recurrent cases had markedly elevated concentrations of alanine aminotransferase (ALT) (P = 0.020) and aspartate aminotransferase (AST) (P = 0.007). Moreover, subgroup analysis showed mild to moderate abnormal concentrations of ALT and AST in recurrent cases. The elevated concentrations of ALT and AST may be recognised as predictive markers for the risk of 'recurrence' of COVID-19, which may provide insights into the prevention and control of COVID-19 in the future.

Elevated transaminases in a COVID-19 positive patient at term of gestation: a case report

BACKGROUND

The coronavirus disease 2019 (COVID-19) pandemic is caused by the severe acute respiratory syndrome 2 virus (SARS-CoV-2) and it is spreading worldwide with an alarming high transmission rate. SARS-CoV-2 usually attacks the lungs causing a wide range of symptoms ranging from mild dyspnea to severe shortness of breath requiring intubation. Elevation of liver transaminases in the patients' sera has been described in up to 53% of the COVID-19 positive patients. The underlying pathogenic mechanisms of the virus on the liver cells are unclear and only few hypotheses are currently available. Data on COVID-19 in pregnant women are lacking and the management of COVID-19 pregnant women is challenging. An elevation of the transaminases during pregnancies infected by SARS-CoV-2 has never been described before.

METHODS

Here we presented the case of a 29 years-old patient at 38 weeks of gestation COVID-19 positive with elevated transaminases.

RESULTS

The patient showed a progressive decrease of transaminases after the delivery of the fetus. We provided details about the daily transaminases trend, the therapy used and the maternal/neonatal outcomes.

CONCLUSIONS

We speculate that in our case the delivery of the fetus contributed to the normalization of the liver enzymes. In patients affected by COVID-19, at term of gestation, with elevated transaminases, delivery of the fetus is an appealing option. If confirmed by larger studies, our proposed management might be incorporated in the obstetrical management guidelines for COVID-19 positive patients.

Drug Repurposing for Candidate SARS-CoV-2 Main Protease Inhibitors by a Novel In Silico Method

The SARS-CoV-2 outbreak caused an unprecedented global public health threat, having a high transmission rate with currently no drugs or vaccines approved. An alternative powerful additional approach to counteract COVID-19 is in silico drug repurposing. The SARS-CoV-2 main protease is essential for viral replication and an attractive drug target. In this study, we used the virtual screening protocol with both long-range and short-range interactions to select candidate SARS-CoV-2 main protease inhibitors. First, the Informational spectrum method applied for small molecules was used for searching the Drugbank database and further followed by molecular docking. After in silico screening of drug space, we identified 57 drugs as potential SARS-CoV-2 main protease inhibitors that we propose for further experimental testing.

Sequence homology between human PARP14 and the SARS-CoV-2 ADP ribose 1'-phosphatase

•There is amino acid sequence homology between the ADP-ribose binding sites of human PARP14 and SARS-CoV-2 ADRP. •This homology is even more pronounced in bat species. •The model proposed highlights the potential of the PARP axis to yield druggable targets for the treatment of COVID-19.

Integrative analysis of miRNA and mRNA sequencing data reveals potential regulatory mechanisms of ACE2 and TMPRSS2

Development of novel approaches for regulating the expression of angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2) is becoming increasingly important within the context of the ongoing COVID-19 pandemic since these enzymes play a crucial role in cell infection. In this work we searched for putative ACE2 and TMPRSS2 expression regulation networks mediated by various miRNA isoforms (isomiR) across different human organs using publicly available paired miRNA/mRNA-sequencing data from The Cancer Genome Atlas (TCGA) project. As a result, we identified several miRNA families targeting ACE2 and TMPRSS2 genes in multiple tissues. In particular, we found that lysine-specific demethylase 5B (JARID1B), encoded by the KDM5B gene, can indirectly affect ACE2 / TMPRSS2 expression by repressing transcription of hsa-let-7e / hsa-mir-125a and hsa-mir-141 / hsa-miR-200 miRNA families which are targeting these genes.

Repositioning of 8565 Existing Drugs for COVID-19

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected over 7.1 million people and led to over 0.4 million deaths. Currently, there is no specific anti-SARS-CoV-2 medication. New drug discovery typically takes more than 10 years. Drug repositioning becomes one of the most feasible approaches for combating COVID-19. This work curates the largest available experimental data set for SARS-CoV-2 or SARS-CoV 3CL (main) protease inhibitors. On the basis of this data set, we develop validated machine learning models with relatively low root-mean-square error to screen 1553 FDA-approved drugs as well as another 7012 investigational or off-market drugs in DrugBank. We found that many existing drugs might be potentially potent to SARS-CoV-2. The druggability of many potent SARS-CoV-2 3CL protease inhibitors is analyzed. This work offers a foundation for further experimental studies of COVID-19 drug repositioning.

Angiotensin converting enzyme: A review on expression profile and its association with human disorders with special focus on SARS-CoV-2 infection

Angiotensin-converting enzyme (ACE) and its homologue, ACE2, have been mostly associated with hypertensive disorder. However, recent pandemia of SARS-CoV-2 has put these proteins at the center of attention, as this virus has been shown to exploit ACE2 protein to enter cells. Clear difference in the response of affected patients to this virus has urged researchers to find the molecular basis and pathophysiology of the cell response to this virus. Different levels of expression and function of ACE proteins, underlying disorders, consumption of certain medications and the existence of certain genomic variants within ACE genes are possible explanations for the observed difference in the response of individuals to the SARS-CoV-2 infection. In the current review, we discuss the putative mechanisms for this observation.

Angiotensin converting enzyme-2 as therapeutic target in COVID-19

The pandemic of coronavirus disease 2019 (COVID-19) is a global health emergency that poses a significant threat to world people's health. This outbreak causes major challenges to healthcare systems. Given the lack of effective treatments or vaccine for it, the identification of novel and safe drugs against COVID-19 infection is an urgent need. Angiotensin-converting enzyme 2 (ACE2) is not only an entry receptor of the SARS-CoV-2 virus, the virus that causes COVID-19, but also can protect from lung injury. In this view, we highlighted potential approaches to address ACE2-mediated SARS-CoV-2 virus, including 1) delivering an excessive soluble form of ACE2 (recombinant human ACE2: rhACE2) and 2) inhibition of the interaction between SARS-CoV-2 virus and ACE2 by some compounds with competitive effects (morphine and codeine). Further clinical trials in this regard can reveal a more definite conclusion against the COVID-19 disaster.

Can ACE2 expression explain SARS-CoV-2 infection of the respiratory epithelia in COVID-19?

Infection with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) leads to coronavirus disease 2019 (COVID-19), which poses an unprecedented worldwide health crisis, and has been declared a pandemic by the World Health Organization (WHO) on March 11, 2020. The angiotensin converting enzyme 2 (ACE2) has been suggested to be the key protein used by SARS-CoV-2 for host cell entry. In their recent work, Lindskog and colleagues (Hikmet et al, 2020) report that ACE2 is expressed at very low protein levels-if at all-in respiratory epithelial cells. Severe COVID-19, however, is characterized by acute respiratory distress syndrome and extensive damage to the alveoli in the lung parenchyma. Then, what is the role of the airway epithelium in the early stages of COVID-19, and which cells need to be studied to characterize the biological mechanisms responsible for the progression to severe disease after initial infection by the novel coronavirus?

Dipeptidyl peptidase-4 (DPP4) inhibition in COVID-19

AIMS

SARS-CoV-2 causes severe respiratory syndrome (COVID-19) with high mortality due to a direct cytotoxic viral effect and a severe systemic inflammation. We are herein discussing a possible novel therapeutic tool for COVID-19.

METHODS

Virus binds to the cell surface receptor ACE2; indeed, recent evidences suggested that SARS-CoV-2 may be using as co-receptor, when entering the cells, the same one used by MERS-Co-V, namely the DPP4/CD26 receptor. The aforementioned observation underlined that mechanism of cell entry is supposedly similar among different coronavirus, that the co-expression of ACE2 and DPP4/CD26 could identify those cells targeted by different human coronaviruses and that clinical complications may be similar.

RESULTS

The DPP4 family/system was implicated in various physiological processes and diseases of the immune system, and DPP4/CD26 is variously expressed on epithelia and endothelia of the systemic vasculature, lung, kidney, small intestine and heart. In particular, DPP4 distribution in the human respiratory tract may facilitate the entrance of the virus into the airway tract itself and could contribute to the development of cytokine storm and immunopathology in causing fatal COVID-19 pneumonia.

CONCLUSIONS

The use of DPP4 inhibitors, such as gliptins, in patients with COVID-19 with, or even without, type 2 diabetes, may offer a simple way to reduce the virus entry and replication into the airways and to hamper the sustained cytokine storm and inflammation within the lung in patients diagnosed with COVID-19 infection.

The Janus kinase 1/2 inhibitor ruxolitinib in COVID-19 with severe systemic hyperinflammation

A subgroup of patients with severe COVID-19 suffers from progression to acute respiratory distress syndrome and multiorgan failure. These patients present with progressive hyperinflammation governed by proinflammatory cytokines. An interdisciplinary COVID-19 work flow was established to detect patients with imminent or full blown hyperinflammation. Using a newly developed COVID-19 Inflammation Score (CIS), patients were prospectively stratified for targeted inhibition of cytokine signalling by the Janus Kinase 1/2 inhibitor ruxolitinib (Rux). Patients were treated with efficacy/toxicity guided step up dosing up to 14 days. Retrospective analysis of CIS reduction and clinical outcome was performed. Out of 105 patients treated between March 30th and April 15th, 2020, 14 patients with a CIS ≥ 10 out of 16 points received Rux over a median of 9 days with a median cumulative dose of 135 mg. A total of 12/14 patients achieved significant reduction of CIS by ≥25% on day 7 with sustained clinical improvement in 11/14 patients without short term red flag warnings of Rux-induced toxicity. Rux treatment for COVID-19 in patients with hyperinflammation is shown to be safe with signals of efficacy in this pilot case series for CRS-intervention to prevent or overcome multiorgan failure. A multicenter phase-II clinical trial has been initiated (NCT04338958).

Structure of Mpro from SARS-CoV-2 and discovery of its inhibitors

A new coronavirus, known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is the aetiological agent responsible for the 2019-2020 viral pneumonia outbreak of coronavirus disease 2019 (COVID-19)^1-4. Currently, there are no targeted therapeutic agents for the treatment of this disease, and effective treatment options remain very limited. Here we describe the results of a programme that aimed to rapidly discover lead compounds for clinical use, by combining structure-assisted drug design, virtual drug screening and high-throughput screening. This programme focused on identifying drug leads that target main protease (M^pro) of SARS-CoV-2: M^pro is a key enzyme of coronaviruses and has a pivotal role in mediating viral replication and transcription, making it an attractive drug target for SARS-CoV-2^5,6. We identified a mechanism-based inhibitor (N3) by computer-aided drug design, and then determined the crystal structure of M^pro of SARS-CoV-2 in complex with this compound. Through a combination of structure-based virtual and high-throughput screening, we assayed more than 10,000 compounds-including approved drugs, drug candidates in clinical trials and other pharmacologically active compounds-as inhibitors of M^pro. Six of these compounds inhibited M^pro, showing half-maximal inhibitory concentration values that ranged from 0.67 to 21.4 μM. One of these compounds (ebselen) also exhibited promising antiviral activity in cell-based assays. Our results demonstrate the efficacy of our screening strategy, which can lead to the rapid discovery of drug leads with clinical potential in response to new infectious diseases for which no specific drugs or vaccines are available.

Structure of Mpro from SARS-CoV-2 and discovery of its inhibitors

A new coronavirus, known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is the aetiological agent responsible for the 2019-2020 viral pneumonia outbreak of coronavirus disease 2019 (COVID-19)^1-4. Currently, there are no targeted therapeutic agents for the treatment of this disease, and effective treatment options remain very limited. Here we describe the results of a programme that aimed to rapidly discover lead compounds for clinical use, by combining structure-assisted drug design, virtual drug screening and high-throughput screening. This programme focused on identifying drug leads that target main protease (M^pro) of SARS-CoV-2: M^pro is a key enzyme of coronaviruses and has a pivotal role in mediating viral replication and transcription, making it an attractive drug target for SARS-CoV-2^5,6. We identified a mechanism-based inhibitor (N3) by computer-aided drug design, and then determined the crystal structure of M^pro of SARS-CoV-2 in complex with this compound. Through a combination of structure-based virtual and high-throughput screening, we assayed more than 10,000 compounds-including approved drugs, drug candidates in clinical trials and other pharmacologically active compounds-as inhibitors of M^pro. Six of these compounds inhibited M^pro, showing half-maximal inhibitory concentration values that ranged from 0.67 to 21.4 μM. One of these compounds (ebselen) also exhibited promising antiviral activity in cell-based assays. Our results demonstrate the efficacy of our screening strategy, which can lead to the rapid discovery of drug leads with clinical potential in response to new infectious diseases for which no specific drugs or vaccines are available.

The Effect of Coronavirus Disease 2019 on Cardiovascular Diseases

Coronavirus disease 2019 (COVID-19) is a global pandemic affecting the world, seen in more than 1,300,000 patients. COVID-19 acts through the angiotensin-converting enzyme 2 (ACE2) receptor. Cardiovascular comorbidities are more common with COVID-19, and nearly 10% of cases develop myocarditis (22% of critical patients). Further research is needed to continue or discontinue ACE inhibitors and angiotensin receptor blockers, which are essential in hypertension and heart failure in COVID-19. Intensive research is promising for the treatment and prevention of COVID-19.

COVID-19 cytokine storm: The anger of inflammation

Patients with COVID-19 who require ICU admission might have the cytokine storm. It is a state of out-of-control release of a variety of inflammatory cytokines. The molecular mechanism of the cytokine storm has not been explored extensively yet. The attachment of SARS-CoV-2 spike glycoprotein with angiotensin-converting enzyme 2 (ACE2), as its cellular receptor, triggers complex molecular events that leads to hyperinflammation. Four molecular axes that may be involved in SARS-CoV-2 driven inflammatory cytokine overproduction are addressed in this work. The virus-mediated down-regulation of ACE2 causes a burst of inflammatory cytokine release through dysregulation of the renin-angiotensin-aldosterone system (ACE/angiotensin II/AT1R axis), attenuation of Mas receptor (ACE2/MasR axis), increased activation of [des-Arg9]-bradykinin (ACE2/bradykinin B1R/DABK axis), and activation of the complement system including C5a and C5b-9 components. The molecular clarification of these axes will elucidate an array of therapeutic strategies to confront the cytokine storm in order to prevent and treat COVID-19 associated acute respiratory distress syndrome.

Potential Inhibitors for Novel Coronavirus Protease Identified by Virtual Screening of 606 Million Compounds

The rapid outbreak of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in China followed by its spread around the world poses a serious global concern for public health. To this date, no specific drugs or vaccines are available to treat SARS-CoV-2 despite its close relation to the SARS-CoV virus that caused a similar epidemic in 2003. Thus, there remains an urgent need for the identification and development of specific antiviral therapeutics against SARS-CoV-2. To conquer viral infections, the inhibition of proteases essential for proteolytic processing of viral polyproteins is a conventional therapeutic strategy. In order to find novel inhibitors, we computationally screened a compound library of over 606 million compounds for binding at the recently solved crystal structure of the main protease (Mpro) of SARS-CoV-2. A screening of such a vast chemical space for SARS-CoV-2 Mpro inhibitors has not been reported before. After shape screening, two docking protocols were applied followed by the determination of molecular descriptors relevant for pharmacokinetics to narrow down the number of initial hits. Next, molecular dynamics simulations were conducted to validate the stability of docked binding modes and comprehensively quantify ligand binding energies. After evaluation of potential off-target binding, we report a list of 12 purchasable compounds, with binding affinity to the target protease that is predicted to be more favorable than that of the cocrystallized peptidomimetic compound. In order to quickly advise ongoing therapeutic intervention for patients, we evaluated approved antiviral drugs and other protease inhibitors to provide a list of nine compounds for drug repurposing. Furthermore, we identified the natural compounds (-)-taxifolin and rhamnetin as potential inhibitors of Mpro. Rhamnetin is already commercially available in pharmacies.

Why Are Lopinavir and Ritonavir Effective against the Newly Emerged Coronavirus 2019? Atomistic Insights into the Inhibitory Mechanisms

Since the emergence of a novel coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first reported from Wuhan, China, neither a specific vaccine nor an antiviral drug against SARS-CoV-2 has become available. However, a combination of two HIV-1 protease inhibitors, lopinavir and ritonavir, has been found to be effective against SARS-CoV, and both drugs could bind well to the SARS-CoV 3C-like protease (SARS-CoV 3CLpro). In this work, molecular complexation between each inhibitor and SARS-CoV-2 3CLpro was studied using all-atom molecular dynamics simulations, free energy calculations, and pair interaction energy analyses based on MM/PB(GB)SA and FMO-MP2/PCM/6-31G* methods. Both anti-HIV drugs interacted well with the residues at the active site of SARS-CoV-2 3CLpro. Ritonavir showed a somewhat higher number atomic contacts, a somewhat higher binding efficiency, and a somewhat higher number of key binding residues compared to lopinavir, which correspond with the slightly lower water accessibility at the 3CLpro active site. In addition, only ritonavir could interact with the oxyanion hole residues N142 and G143 via the formation of two hydrogen bonds. The interactions in terms of electrostatics, dispersion, and charge transfer played an important role in the drug binding. The obtained results demonstrated how repurposed anti-HIV drugs could be used to combat COVID-19.

Angiotensin-converting enzyme 2 in severe acute respiratory syndrome coronavirus and SARS-CoV-2: A double-edged sword?

Human angiotensin-converting enzyme 2 (ACE2) facilitates cellular entry of severe acute respiratory syndrome coronavirus (SARS-CoV) and SARS-CoV-2 as their common receptor. During infection, ACE2-expressing tissues become direct targets, resulting in serious pathological changes and progressive multiple organ failure or even death in severe cases. However, as an essential component of renin-angiotensin system (RAS), ACE2 confers protective effects in physiological circumstance, including maintaining cardiovascular homeostasis, fluid, and electrolyte balance. The absence of protective role of ACE2 leads to dysregulated RAS and thus acute changes under multiple pathological scenarios including SARS. This potentially shared mechanism may also be the molecular explanation for pathogenesis driven by SARS-CoV-2. We reasonably speculate several potential directions of clinical management including host-directed therapies aiming to restore dysregulated RAS caused by ACE2 deficiency. Enriched knowledge of ACE2 learned from SARS and COVID-19 outbreaks can provide, despite their inherent tragedy, informative clues for emerging pandemic preparedness.

COVID-19, ACE2, and the cardiovascular consequences

The novel SARS coronavirus SARS-CoV-2 pandemic may be particularly deleterious to patients with underlying cardiovascular disease (CVD). The mechanism for SARS-CoV-2 infection is the requisite binding of the virus to the membrane-bound form of angiotensin-converting enzyme 2 (ACE2) and internalization of the complex by the host cell. Recognition that ACE2 is the coreceptor for the coronavirus has prompted new therapeutic approaches to block the enzyme or reduce its expression to prevent the cellular entry and SARS-CoV-2 infection in tissues that express ACE2 including lung, heart, kidney, brain, and gut. ACE2, however, is a key enzymatic component of the renin-angiotensin-aldosterone system (RAAS); ACE2 degrades ANG II, a peptide with multiple actions that promote CVD, and generates Ang-(1-7), which antagonizes the effects of ANG II. Moreover, experimental evidence suggests that RAAS blockade by ACE inhibitors, ANG II type 1 receptor antagonists, and mineralocorticoid antagonists, as well as statins, enhance ACE2 which, in part, contributes to the benefit of these regimens. In lieu of the fact that many older patients with hypertension or other CVDs are routinely treated with RAAS blockers and statins, new clinical concerns have developed regarding whether these patients are at greater risk for SARS-CoV-2 infection, whether RAAS and statin therapy should be discontinued, and the potential consequences of RAAS blockade to COVID-19-related pathologies such as acute and chronic respiratory disease. The current perspective critically examines the evidence for ACE2 regulation by RAAS blockade and statins, the cardiovascular benefits of ACE2, and whether ACE2 blockade is a viable approach to attenuate COVID-19.

ACE2: The key Molecule for Understanding the Pathophysiology of Severe and Critical Conditions of COVID-19: Demon or Angel?

Recently, the SARS-CoV-2 induced disease COVID-19 has spread all over the world. Nearly 20% of the patients have severe or critical conditions. SARS-CoV-2 exploits ACE2 for host cell entry. ACE2 plays an essential role in the renin–angiotensin–aldosterone system (RAAS), which regulates blood pressure and fluid balance. ACE2 also protects organs from inflammatory injuries and regulates intestinal functions. ACE2 can be shed by two proteases, ADAM17 and TMPRSS2. TMPRSS2-cleaved ACE2 allows SARS-CoV-2 cell entry, whereas ADAM17-cleaved ACE2 offers protection to organs. SARS-CoV-2 infection-caused ACE2 dysfunction worsens COVID-19 and could initiate multi-organ failure. Here, we will explain the role of ACE2 in the pathogenesis of severe and critical conditions of COVID-19 and discuss auspicious strategies for controlling the disease.

Susceptibility of the Elderly to SARS-CoV-2 Infection: ACE-2 Overexpression, Shedding, and Antibody-dependent Enhancement (ADE)

The world is currently facing a serious SARS-CoV-2 infection pandemic. </mac_aq>This virus is a new isolate of coronavirus, and the current infection crisis has surpassed the SARS and MERS epidemics</mac_aq> that occurred in 2002 and 2013, respectively. SARS-CoV-2 has currently infected more than 142,000 people, causing </mac_aq>5,000 deaths and spreading across more than 130 </mac_aq>countries worldwide. The spreading capacity of the virus clearly demonstrates the potential threat </mac_aq>of respiratory viruses to human health, thereby reiterating to the governments around the world that preventive </mac_aq>health policies and scientific research are pivotal to overcoming the crisis. Coronavirus disease (COVID-19) causes flu-like symptoms in most cases. However, approximately 15% of the patients need hospitalization, and 5% require assisted ventilation, depending on the cohorts studied. What is intriguing, however, is the higher susceptibility of the elderly, especially individuals who are older than 60 years of age, and have comorbidities, including hypertension, diabetes, and heart disease. In fact, the death rate in this group may be up to 10-12%. Interestingly, children are somehow less susceptible and are not considered as a risk group. Therefore, in this review, we discuss some possible molecular and cellular mechanisms by virtue of which the elderly subjects may be more susceptible to severe COVID-19. Toward this, we raise two main </mac_aq>points, i) increased ACE-2 expression in pulmonary and heart tissues in users of chronic angiotensin 1 </mac_aq>receptor (AT1R) blockers; and ii) antibody-dependent enhancement (ADE) after previous exposure to other circulating coronaviruses. We believe that these points are pivotal for a better understanding of the pathogenesis of severe COVID-19, and must be carefully addressed by physicians and scientists in the field.

The autoimmune response elicited by mouse hepatitis virus (MHV-A59) infection is modulated by liver tryptophan-2,3-dioxygenase (TDO)

In a previous work we demonstrated that inhibition of mouse indoleamine 2,3-dioxygenase (IDO) by methyltryptophan (MT) exacerbated the pathological actions of mouse hepatitis virus (MHV-A59) infection, suggesting that tryptophan (TRP) catabolism was involved in viral effects. Since there is a second enzyme that dioxygenates TRP, tryptophan-2, 3-dioxygenase (TDO), which is mainly located in liver, we decided to study its role in our model of MHV-infection. Results showed that in vivo TDO inhibition by LM10, a derivative of 3-(2-(pyridyl) ethenyl) indole, resulted in a decrease of anti- MHV Ab titers induced by the virus infection. Besides, a reduction of some alarmin release, i.e, uric acid and high-mobility group box1 protein (HMGB1), was observed. Accordingly, since alarmin liberation was related to the expression of autoantibodies (autoAb) to fumarylacetoacetate hydrolase (FAH), these autoAb also diminished. Moreover, PCR results indicated that TDO inhibition did not abolish viral replication. Furthermore, histological liver examination did not reveal strong pathologies, whereas mouse survival was hundred percent in control as well as in MHV-infected mice treated with LM10. Data presented in this work indicate that in spite of the various TDO actions already described, specific TDO blockage could also restrain some MHV actions, mainly suppressing autoimmune reactions. Such results should prompt further experiments with various viruses to confirm the possible use of a TDO inhibitor such as LM-10 to treat either viral infections or even autoimmune diseases triggered by a viral infection.

TMPRSS2: A potential target for treatment of influenza virus and coronavirus infections

Influenza virus and coronavirus epidemics or pandemics have occurred in succession worldwide throughout the early 21st century. These epidemics or pandemics pose a major threat to human health. Here, we outline a critical role of the host cell protease TMPRSS2 in influenza virus and coronavirus infections and highlight an antiviral therapeutic strategy targeting TMPRSS2.

The tetraspanin CD9 facilitates MERS-coronavirus entry by scaffolding host cell receptors and proteases

Infection by enveloped coronaviruses (CoVs) initiates with viral spike (S) proteins binding to cellular receptors, and is followed by proteolytic cleavage of receptor-bound S proteins, which prompts S protein-mediated virus-cell membrane fusion. Infection therefore requires close proximity of receptors and proteases. We considered whether tetraspanins, scaffolding proteins known to facilitate CoV infections, hold receptors and proteases together on cell membranes. Using knockout cell lines, we found that the tetraspanin CD9, but not the tetraspanin CD81, formed cell-surface complexes of dipeptidyl peptidase 4 (DPP4), the MERS-CoV receptor, and the type II transmembrane serine protease (TTSP) member TMPRSS2, a CoV-activating protease. This CD9-facilitated condensation of receptors and proteases allowed MERS-CoV pseudoviruses to enter cells rapidly and efficiently. Without CD9, MERS-CoV viruses were not activated by TTSPs, and they trafficked into endosomes to be cleaved much later and less efficiently by cathepsins. Thus, we identified DPP4:CD9:TTSP as the protein complexes necessary for early, efficient MERS-CoV entry. To evaluate the importance of these complexes in an in vivo CoV infection model, we used recombinant Adenovirus 5 (rAd5) vectors to express human DPP4 in mouse lungs, thereby sensitizing the animals to MERS-CoV infection. When the rAd5-hDPP4 vectors co-expressed small RNAs silencing Cd9 or Tmprss2, the animals were significantly less susceptible, indicating that CD9 and TMPRSS2 facilitated robust in vivo MERS-CoV infection of mouse lungs. Furthermore, the S proteins of virulent mouse-adapted MERS-CoVs acquired a CD9-dependent cell entry character, suggesting that CD9 is a selective agent in the evolution of CoV virulence.

[Clinical and Biological Character in Mouse Models for Middle East Respiratory Syndrome Generated by Transduction with Different Doses of DPP4 Molecule]

In this study, we evaluated the difference ot biological characteristics in the MERS-CoV infected mice model in prior to transduction with different dosage of human DPP4. Firstly, we transduced different dosage of DPP4 (high or low) into mice, and then challenged them with MERS-CoV in order to establish the model. After establishment of mice model, we observed the clinical signs of disease, virus replication, immunopathogenesis and antibody response. The results indicated that the infected mice showed typical pneumonia, virus replication, histological lesions, and neutralizing antibody production. Moreover, the high dosage group was superior to the low dosage group. Fourteen days after infection, the specific antibody to virus structural protein and neutralizing antibody were analyzed, the high dosage group induced higher level antibody. In summary, the MERS-CoV infected mice model were established prior transduction with DPP4, and the level of DPP4 influenced the clinical signs of disease, virus replication and antibody response in this model.

Targeting zoonotic viruses: Structure-based inhibition of the 3C-like protease from bat coronavirus HKU4--The likely reservoir host to the human coronavirus that causes Middle East Respiratory Syndrome (MERS)

The bat coronavirus HKU4 belongs to the same 2c lineage as that of the deadly Middle East Respiratory Syndrome coronavirus (MERS-CoV) and shows high sequence similarity, therefore potentiating a threat to the human population through a zoonotic shift or 'spill over' event. To date, there are no effective vaccines or antiviral treatments available that are capable of limiting the pathogenesis of any human coronaviral infection. An attractive target for the development of anti-coronaviral therapeutics is the 3C-like protease (3CL(pro)), which is essential for the progression of the coronaviral life cycle. Herein, we report the screening results of a small, 230-member peptidomimetic library against HKU4-CoV 3CL(pro) and the identification of 43 peptidomimetic compounds showing good to excellent inhibitory potency of HKU4-CoV 3CL(pro) with IC50 values ranging from low micromolar to sub-micromolar. We established structure-activity relationships (SARs) describing the important ligand-based features required for potent HKU4-CoV 3CL(pro) inhibition and identified a seemingly favored peptidic backbone for HKU4-CoV 3CL(pro) inhibition. To investigate this, a molecular sub-structural analysis of the most potent HKU4-CoV 3CL(pro) inhibitor was accomplished by the synthesis and testing of the lead peptidomimetic inhibitor's sub-structural components, confirming the activity of the favored backbone (22A) identified via SAR analysis. In order to elucidate the structural reasons for such potent HKU4-CoV 3CL(pro) inhibition by the peptidomimetics having the 22A backbone, we determined the X-ray structures of HKU4-CoV 3CL(pro) in complex with three peptidomimetic inhibitors. Sequence alignment of HKU4-CoV 3CL(pro), and two other lineage C Betacoronaviruses 3CL(pro)'s, HKU5-CoV and MERS-CoV 3CL(pro), show that the active site residues of HKU4-CoV 3CL(pro) that participate in inhibitor binding are conserved in HKU5-CoV and MERS-CoV 3CL(pro). Furthermore, we assayed our most potent HKU4-CoV 3CL(pro) inhibitor for inhibition of HKU5-CoV 3CL(pro) and found it to have sub-micromolar inhibitory activity (IC50=0.54±0.03μM). The X-ray structures and SAR analysis reveal critical insights into the structure and inhibition of HKU4-CoV 3CL(pro), providing fundamental knowledge that may be exploited in the development of anti-coronaviral therapeutics for coronaviruses emerging from zoonotic reservoirs.

Identification of the functional domain of the porcine epidemic diarrhoea virus receptor

Porcine aminopeptidase N (pAPN) is a functional receptor for porcine epidemic diarrhoea virus (PEDV). Although PEDV is known to use the pAPN as the major receptor for cell entry, the crucial domain of the pAPN that interacts with the PEDV is still unknown. In the present study, in order to determine the crucial domain of the pAPN, the extracellular domain of pAPN was divided into three subdomains named SPA, SPB and SPC, based on its secondary structure. Recombinant plasmid pcDNA3.1 expressing SPA, SPB and SPC was constructed and introduced into Madin-Darby canine kidney (MDCK) cells by transfection. Following the detection of PEDV infection in transfected MDCK cells after PEDV challenge, we clearly demonstrated that the SPC subdomain plays a key role in cell entry of PEDV and its expression permits PEDV growth in transfected MDCK cells, while virus propagation can be inhibited by anti-SPC serum, indicating that the SPC subdomain appears to be a crucial functional domain in contributing to efficient PEDV infection.

Association of host tropism of Middle East syndrome coronavirus with the amino acid structure of host cell receptor dipeptidyl peptidase 4

The Middle East syndrome coronavirus (MERS-CoV) is a recently emerging betacoronavirus with high fatality. Recently, dipeptidyle peptidase (CD26, DPP4) was identified as the host cell receptor for MERS-CoV. Interestingly, despite of common presence of DPP4 receptors the binding and infection of various cells shows imminent variability. In this report, we provide a tool for prediction of the host tropism of the virus based on the host receptor binding interface. We found out that, in the binding of MERS-CoV to cells the amino acid residues in lancets 4 and 5 of DPP4 receptor, namely K267, Q286, T288, R317, R336, Q344 A291, L294, and I295 are involved. Changes in these residues correspond to profound decrease in virus binding to cells. The nine residues at the interface between the virus spikes and the lancets 4 and 5 of host DPP4 can be used as a predictive tool for the host tropism and virus affinity to host cell receptors.

Porcine epidemic diarrhea virus induces caspase-independent apoptosis through activation of mitochondrial apoptosis-inducing factor

The present study sought to investigate whether porcine epidemic diarrhea virus (PEDV) induces apoptosis and to elucidate the mechanisms associated with apoptotic cell death after PEDV infection. PEDV-infected cells showed evidence of apoptosis in vitro and in vivo. However, experimental data indicated that the caspase cascade is not involved in PEDV-induced apoptotic cell death. Interestingly, mitochondrial apoptosis-inducing factor (AIF) was found to translocate to the nucleus during PEDV infection, and AIF relocalization was completely abrogated by the presence of cyclosporin A (CsA), an inhibitor of cyclophilin D (CypD) that is an essential component of the mitochondrial permeabilization transition pore (mPTP) complex. CsA treatment resulted in significant inhibition of PEDV-triggered apoptosis and suppressed PEDV replication. Furthermore, direct inhibition of AIF strongly impaired PEDV infection and virus-induced apoptosis. Altogether, our results indicate that a caspase-independent mitochondrial AIF-mediated pathway plays a central role in PEDV-induced apoptosis to facilitate viral replication and pathogenesis.

Human coronavirus-induced neuronal programmed cell death is cyclophilin d dependent and potentially caspase dispensable

Human coronaviruses (HCoV) are recognized respiratory pathogens. Some HCoV strains, including HCoV-OC43, can invade the central nervous system, where they infect neurons, with unclear consequences. We have previously reported that HCoV-OC43 infection of human neurons activates the unfolded-protein response and caspase-3 and induces cell death and that the viral spike (S) glycoprotein is involved in the process. We now report on underlying mechanisms associated with the induction of programmed cell death (PCD) after infection by the reference HCoV-OC43 virus (rOC/ATCC) and a more neurovirulent and cytotoxic HCoV-OC43 variant harboring two point mutations in the S glycoprotein (rOC/U(S183-241)). Even though caspase-3 and caspase-9 were both activated after infection, the use of caspase inhibitors neither reduced nor delayed virus-induced PCD, suggesting that these proteases are not essential in the process. On the other hand, the proapoptotic proteins BAX, cytochrome c (CytC), and apoptosis-inducing factor (AIF) were relocalized toward the mitochondria, cytosol, and nucleus, respectively, after infection by both virus variants. Moreover, LA-N-5 neuronal cells treated with cyclosporine (CsA), an inhibitor of the mitochondrial permeabilization transition pore (mPTP), or knocked down for cyclophilin D (CypD) were completely protected from rOC/ATCC-induced neuronal PCD, underlining the involvement of CypD in the process. On the other hand, CsA and CypD knockdown had moderate effects on rOC/U(S183-241)-induced PCD. In conclusion, our results are consistent with mitochondrial AIF and cyclophilin D being central in HCoV-OC43-induced PCD, while caspases appear not to be essential.

Picornaviral 3C protease inhibitors and the dual 3C protease/coronaviral 3C-like protease inhibitors

IMPORTANCE OF THE FIELD

Picornaviruses are small non-enveloped RNA viruses with genomic RNA of 7500 - 8000 nucleotides, whereas coronaviruses (CoV) are RNA viruses with larger genome of 27 - 32 kb. Both types of viruses translate their genetic information into polyprotein precursors that are processed by virally encoded 3C proteases (3C(pro)) and 3C-like proteases (3CL(pro)), respectively, to generate functional viral proteins. The most studied human rhinoviruses (HRV) belonging to picornaviridae family are the main etiologic agents of the common cold. Due to lack of effective drugs, 3C(pro) has served as an excellent target for anti-viral intervention and considerable efforts have been made in the development of inhibitors. Interestingly, the inhibitors of 3C(pro) cannot inhibit 3CL(pro) potently without modification due to subtle differences in their active-site structures, but a group of common inhibitors against 3C(pro) and 3CL(pro) were found recently.

AREAS COVERED IN THIS REVIEW

The inhibitors against 3C(pro) reported in the literatures and patents, with a focus on those inhibiting HRV and the dual picornaviral 3C(pro)/coronaviral 3CL(pro) inhibitors, are summarized in this review.

WHAT THE READERS WILL GAIN

Readers will rapidly gain an overview of the individual and dual 3C(pro) inhibitors and the structural basis for discriminating them.

TAKE HOME MESSAGE

In the future, more selective potent inhibitors against each protease and dual inhibitors against both proteases can be further developed to treat the diseases caused by picornaviruses and CoV.

[Porcine aminopeptidase N is a functional receptor for the PEDV coronavirus]

Porcine epidemic diarrhea virus (PEDV) causes lethal diarrhea in piglets that leads to great economic losses in East Asia. It was reported that aminopeptidase N (APN) was the receptor for Transmissible gastroenteritis virus (TGEV), Human coronavirus 229E (HCoV-229E) and Feline coronavirus (FeCoV) which all belonged to group I coronavirus including PEDV. It was also confirmed previously that porcine aminopeptidase N (pAPN) could bind to PEDV, and anti-pAPN antibodies could inhibit the combination. To investigate whether pAPN was a receptor for PEDV, we transfected MDCK cells with porcine aminopeptidase (pAPN) cDNA and this enabled non-susceptible cells to support PEDV replication and serial viral propagation. Moreover, the infection was blocked by antibodies against pAPN, implying the critical role of pAPN during virus entry. In addition, immunofluorescence assays for detection of pAPN and PEDV antigens, together with neutralization assays using antibodies against pAPN, further confirmed the correlation between pAPN expression and viral replication in pAPN-transfected MDCK cells. These results indicated that pAPN is a functional receptor for PEDV.

Canine coronavirus induces apoptosis in cultured cells

Canine coronavirus (CCoV) is widespread in dogs in several countries and causes mild enteric illness evolving to severe enteritis in young pups.

In in vitro cultures canine coronaviruses generally induce extensive cell death, however nature of the events leading to cell death remains largely unknown.

We analysed the induction of cytopathic effect by CCoV in a canine fibrosarcoma cell line (A-72) in order to characterize the apoptotic effect in homologous cell system.

Following CCoV infection A-72 cell line, which is permissive to CCoV, showed reduced growth rate, as detected by MTT assay, a standard colorimetric assay for measuring cellular proliferation, and underwent to apoptotic death. Starting from 24 h after CCoV infection, cells morphology appeared dramatically changed, with cells rounding and detachment from culture surface. Morphologic and biochemical features of apoptosis, such as blebbing of the plasma membrane, translocation of phosphatidilserine to cell surface and annexin V positive staining, nuclear fragmentation, apoptotic bodies formation and DNA laddering, were detected in CCoV-infected cells. Propidium iodide staining of infected culture indicated the appearance of hypodiploid DNA peak corresponding to apoptotic cell population. Commonly to other animal coronavirus infection caspase-3 is likely to contribute to the execution phase of apoptosis induced by CCoV in A-72 cells since we found activation of enzymatic activity as well as procaspase-3 activating cleavage. Apoptotic death of infected cells is detrimental as it causes cell and tissue destruction as well as inflammatory responses. Therefore in the case of CCoV associated gastroenteritis, apoptosis of epithelial mucosa cells may be responsible for pathology induced by CCoV infection.