key: cord-0709260-j1uo8qmf
authors: Crimi, Ettore; Benincasa, Giuditta; Figueroa-Marrero, Neisaliz; Galdiero, Massimiliano; Napoli, Claudio
title: Epigenetic susceptibility to severe respiratory viral infections: pathogenic and therapeutic implications: a narrative review
date: 2020-08-20
journal: Br J Anaesth
DOI: 10.1016/j.bja.2020.06.060
sha: 5e303814ad0fd63c593a14c4c27901e932cff53e
doc_id: 709260
cord_uid: j1uo8qmf

The emergence of highly pathogenic strains of influenza virus and coronavirus (CoV) has been responsible for large epidemic and pandemic outbreaks characterised by severe pulmonary illness associated with high morbidity and mortality. One major challenge for critical care is to stratify and minimise the risk of multi-organ failure during the stay in the intensive care unit (ICU). Epigenetic-sensitive mechanisms, including deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) methylation, histone modifications, and non-coding RNAs may lead to perturbations of the host immune-related transcriptional programmes by regulating chromatin structure and gene expression patterns. Viruses causing severe pulmonary illness can use epigenetic-regulated mechanisms during host–pathogen interaction to interfere with innate and adaptive immunity, adequacy of inflammatory response, and overall outcome of viral infections. For example, Middle East respiratory syndrome-CoV and H5N1 can affect host antigen presentation through DNA methylation and histone modifications. The same mechanisms would presumably occur in patients with coronavirus disease 2019, in which tocilizumab may epigenetically reduce microvascular damage. Targeting epigenetic pathways by immune modulators (e.g. tocilizumab) or repurposed drugs (e.g. statins) may provide novel therapeutic opportunities to control viral–host interaction during critical illness. In this article, we provide an update on epigenetic-sensitive mechanisms and repurposed drugs interfering with epigenetic pathways which may be clinically suitable for risk stratification and beneficial for treatment of patients affected by severe viral respiratory infections.

influenza, and influenza A virus subtype H5N1 or avian influenza) and coronavirus (CoV) (i.e. severe acute respiratory syndrome [SARS]-CoV, Middle East respiratory syndrome [MERS]-CoV, and SARS-CoV-2) responsible for pandemic infections associated with high morbidity and mortality. 1e5 These viruses may cause a wide spectrum of respiratory manifestations associated with massive inflammatory cell infiltration and proinflammatory cytokine/chemokine release resulting in acute lung injury (ALI); acute respiratory distress syndrome (ARDS); and, ultimately, death from multi-organ failure (MOF). 6e8 Molecular mechanisms regulating virusehost interactions can significantly affect the degree and adequacy of both immune and inflammatory responses influencing clinical outcomes. 9e11 For the critical care physicians, to identify and prevent the occurrence of this exuberant inflammatory response and to stratify the risk of MOF in the intensive care unit (ICU) are still major challenges. 12 Epigenetics may influence host susceptibility to such viral infections. 13 Deoxyribonucleic acid (DNA) methylation, ribonucleic acid (RNA) methylation, histone tail changes, and also non-coding RNAs are heritable and acquired modifications able to alter gene expression at different levels without any changes in the primary DNA sequence. Epigenetic mechanisms, by regulating chromatin structure and gene expression patterns, modulate host immunity and inflammatory response. 14 In critical illness, such epigenetic modifications can promote the release of proinflammatory cytokines and activation of inflammatory cells, responsible for oxidative stress, endothelial dysfunction, apoptosis, and MOF. 15 Epigenetics can also regulate the interaction between host and multidrug-resistant bacteria. 16 The interaction of viruses with host cells can cause perturbations of transcriptional programmes involving such epigenetic mechanisms leading to viral shedding and inadequate immune response. 13 Middle East respiratory syndrome-CoV and H5N1 infections can antagonise the host immune response by modulating antigen presentation through DNA methylation and histone modifications. 17e20 Similar mechanisms would occur during coronavirus disease 2019 . 21, 22 Indeed, advanced bioinformatic tools have predicted the possibility of using microRNAs (miRNAs) to inhibit infections caused by COVID-19, SARS-CoV, and MERS-CoV by inhibiting the translation of viral proteins and viral replication. 21 As some epigenetic changes can be reversed by small agents, known as 'epidrugs', or alternatively, epigenetic pathways can be interfered by immune modulators, they might provide useful drug targets to ameliorate the clinical outcome during viral respiratory infections. 23, 24 Ongoing trials will answer to this possible clinical application. The goal of the review was to provide an appropriate pathogenic scenario in which epigenetic-sensitive mechanisms and epidrugs may be clinically useful to stratify risk and treatment of patients in ICU affected by severe viral respiratory infections.

Influenza viruses are enveloped, single-stranded RNA viruses classified into three major serotypes: A, B, and C. Influenza A viruses, the most extensively studied, are further classified based on the different subtypes of the two surface glycoproteins: haemagglutinin (H1eH18) and neuraminidase (N1eN11) which facilitate virus binding to host respiratory epithelial cells via a sialic acid receptor and virions released from cells, respectively. 25 Avian influenza A virus H5N1 26À28 and swine influenza A H1N1 29À34 infections have caused acute respiratory failure secondary to severe pneumonia and ARDS. The highly pathogenic avian influenza A virus H5N1, first described in 1996, caused severe pneumonia with high mortality (more than 60%), secondary to ARDS and MOF. 26e28 Risks factors for severe influenza A H1N1 infection included pregnancy, Table 1 Clinical and immunological features of viral respiratory infections by influenza viruses. 36e44 COPD, chronic obstructive pulmonary disease; CR, conventional radiograph; CT, computed tomography; GGO, ground glass opacity; HF, heart failure; IFNg, interferon g; IL-1 RA, interleukin-1 receptor antagonist protein; IP-10, interferon-g-inducible protein-10; MCP-1, monocyte chemoattractant protein-1; MIP 1-b, macrophage inflammatory protein 1-B; TLR-3, Toll-like receptor Type 3; TNF-a, tumour necrosis factor-alpha. obesity, asthma, and chronic obstructive pulmonary disease (COPD). 29e34 Mitigation of the pathogenicity of the pandemic virus was probably caused by the presence of a cross-reactive cell response against this virus, which was boosted by seasonal vaccination. 35 In Table 1, we summarised clinical and  immunological features of viral respiratory infections by  influenza viruses. 36e44 Coronaviruses Coronaviruses, named after their crown-like structure, are enveloped, positive-sense RNA viruses, containing the largest known genome amongst RNA viruses. The CoV genome encodes for 16 non-structural proteins, which form the viral replicase transcriptase complex, and four essential structural proteins, involved in the host immune response and virion assembly: the spike (S) protein, responsible for receptor binding and viral entry into the host cell; the membrane (M) and envelope (E) proteins, responsible for virus assembly and release; and the nucleocapsid (N) protein, important for RNA synthesis and its final packaging into the viral particles. 45 The genome sequence of SARS-CoV-2 is about 79% identical to the SARS-CoV and 50% to the MERS-CoV. 46 These viruses cause severe respiratory infections (Table 2) . 47e60 Older adults with co-morbidities, especially cardiovascular diseases, diabetes, obesity, renal failure, and COPD, are at higher risk of severe disease. 51, 56 ICU admission for organ support occurs in about 20e30%, 5e36%, and 50e89% of patients infected with SARS-CoV, SARS-CoV-2, and MERS-CoV, respectively. 3,51e53,56 Currently, global public health is facing the COVID-19 pandemic as the third CoV crisis in less than 20 yr (https://www.nih.gov/health-information/coronavirus).

Coronaviruses are capable of infecting several other organs, as demonstrated by the presence of SARS-CoV in circulating immune cells, neurones, intestinal mucosa, and epithelium of renal distal tubules. 61 Coronavirusesehost interaction can influence susceptibility to CoV infection and progression to severe disease. 3, 11 After entering the body via the respiratory system, a critical step for cell entry and infection is the binding of the envelope S glycoprotein to the epithelial cells through specific receptors. The S protein of the SARS-CoV and SARS-CoV-2 binds to the angiotensinconverting enzyme 2 (ACE2) molecule present on cells through the receptor-binding domain, 62, 63 whilst MERS-CoV binds to the host cell protein dipeptidyl peptidase 4. 64 After binding to the host, the S protein needs to be activated by a cellular protease, the transmembrane protease serine 2, which cleaves S in two subunits liberating the fusion peptide that mediates the fusion of the viral envelope with the cellular membrane. Differences in the structural and dynamic state of the receptor-binding domain 65 and S protein priming 66 between SARS-CoV and SARS-CoV-2 cause higher ACE2-binding affinity of the SARS-CoV-2 and favour its evasion of the immune surveillance, 64 suggesting a potential explanation of the higher SARS-CoV-2 infectivity. 63 Angiotensin-converting enzyme 2 can play a protective role in lung injury, 67 and its downregulation by SARS-CoV can contribute to progression to severe lung injury. 68 On the contrary, MERS-CoV regulates dipeptidyl peptidase 4 receptor in the lungs of smokers and COPD, and this could explain their susceptibility to severe disease. 69 To survive in the host cells, the CoVs adopt multiple strategies to evade detection by the host immune system, allowing active virus replication. The virus can downregulate genes involved in the antigen presentation, such as retinoic-acidinducible gene and melanoma differentiation-associated protein 5, and interfere with intracellular signalling pathways through structural (proteins M and N) and non-structural proteins, so delaying interferon (IFN) expression. 3, 17, 70, 71 Ultimately, a delayed but excessive reaction of the immune system with an uncontrolled expression of cytokines and chemokines (the so-called cytokine storm) associated with virus-induced cytopathic effects will result in lung epithelial and endothelial cell apoptosis and activation of the coagulation cascade, leading to vascular leakage; alveolar oedema; microvascular thrombosis; and, later, cell proliferation with pulmonary fibrosis. 3, 11, 47 Cytokine storm in such patients is associated with more severe lung injury, ICU admission, and worse outcome. 3, 51, 71 To date, no definitive treatment for 

Viruses causing severe pulmonary illness can use three epigenetic-regulated ways during hostepathogen interaction: (i) they can affect host DNA methylation signatures and miR-NAs regulating a cassette of genes underlying innate and adaptive antiviral responses; (ii) they can encode for viral proteins that directly interact with the host modified histones; and (iii) they can manipulate the host miRNA processing nuclear machinery to encode viral non-canonical miRNA-like RNA fragments (v-miRNAs) regulating the viral life cycle and immune response. 73 Here, we focus on epigenetic-sensitive mechanisms by which H5N1 and SARS-CoV-2 may affect susceptibility to pulmonary illness by interfering with both innate and adaptive immune responses in humans 74,75 ( Fig. 1 and Table 3 ).

By combining multi-omics data, H5N1 antagonised the early host antiviral response by altering histone methylation at Type I IFN-sensitive genes. 18 In detail, NS1 viral protein was associated with parallel increased H3K27me3 (repressive mark) and decreased H3K4me3 (active mark) levels favouring a heterochromatin state surrounding the SMAD9L, CFHR1, and DDX58 genes in human airway cells. 18 Viral non-canonical miRNA-like RNA fragments induced cytokine storm and high mortality 76 ; however, v-miRNA biogenesis and function remain to be clarified. 81 Overall, the virus skill to produce functional miRNAs can be also exploited to construct delivery systems of miRNAs based on RNA viruses as molecular vectors. 82

Severe acute respiratory syndrome coronavirus 2

The high transmissibility and asymptomatic infection rates of SARS-CoV-2 may be caused by a more efficient virus replication and reduced IFN production in lung tissues. 83 As both SARS-CoV-2 and MERS can reprogramme the host epigenome, we hypothesise a possible role for epigenetic drivers underlying susceptibility to COVID-19. Sawalha and colleagues 77 have proposed oxidativestress-induced epigenetic pathways linked to ACE2 deregulation to increase susceptibility and severity of COVID-19 in patients affected by systemic lupus erythematosus (SLE). Indeed, the ACE2 gene CpG hypomethylation status characterising SLE patients could be exacerbated upon SARS-CoV-2 infection leading to further ACE2 protein overexpression in T cells, thus promoting viral infections and dissemination. 77 Disease-related epigenetic perturbations might be hotspots favouring viral infection and provide risk biomarkers useful to stratify sensitiveness to infection and disease severity in patients more prone to disseminate SARS-CoV-2 infection. Consistent with this, a bioinformatic analysis focusing on ACE2 gene has supported the hypothesis for which DNA methylation signatures are dependent on host cell type and gender and age, which are risk factors associated with increased susceptibility to COVID-19 and poor prognosis. 84 

Patients affected by COVID-19 are at higher risk of thromboembolic events and disseminated intravascular coagulation. 85 As evidence of neutrophil lung infiltration, Barnes and colleagues 78 have emphasised the key role of NETosis in contributing to organ damage and mortality of patients affected by COVID-19. Physiologically, NETosis is a form of innate immunity, in which the neutrophil cell death is guided from histone H3 modifications and release of neutrophil extracellular traps (NETs), complexes of DNA fibres, histones, and proteins aimed to provide a scaffold for platelet adhesion and aggregation to entrap pathogens and avoid their diffusion. 86 Moreover, NETs can induce macrophages to secrete IL1B to further sustain the signalling loop between macrophages and neutrophils, leading to progressive inflammatory damage. Previously, NETosis dysregulation was linked to thrombotic events, 86 ARDS, pulmonary inflammation, and extensive lung damage. 87 Interestingly, there is evidence for which heparin can dismantle NETs and prevent histone-induced platelet aggregation. This might represent the molecular basis for which heparin treatment reduces mortality in subjects affected by severe COVID-19, which develop sepsis-induced coagulopathy. 88 Thus, deoxyribonuclease I-mediated degradation of NETs could provide a therapeutic avenue to suppress excess injury in patients severely affected by COVID-19. 89 

The epitranscriptome of SARS-CoV-2 was analaysed as a possible strategy to dissect the hidden layer of viral regulation. By using nanopore direct RNA sequencing, almost 41 RNA modification sites, mostly located in the AAGAA motif on viral transcripts with shorter poly(A) tails, have been suggested. 90 As poly(A) tails play a relevant role in RNA turnover and stability, the proposed modifications may represent one of the molecular mechanisms by which SARS-CoV-2 evades the host immune response and indices the cytokine storm. 90 Besides, the authors did not identify what type of RNA modifications occur at these sites and the mechanisms underlying COVID-19 pathogenesis. 90

Nowadays, the emergence of drug-resistant pathogens continuously increases, thus the discovery of novel drugs or the repositioning of already-approved drugs is needed. 16 Epitherapy may provide further therapeutic opportunities to control viralehost interaction during critical illness. 91 In particular, the current emergence of COVID-19 is guiding researchers towards the possible repurposing of Food and Drug Administration (FDA)-approved epidrugs, 92 including metformin and statins, which may be effective against the novel SARS-CoV-2 infection. Here, we give an update on clinical evidence about the usefulness of novel and FDA-approved drugs interfering with epigenetic pathways, which were applied to ICU patients affected by highly pathogenic strains of influenza virus and CoV, with a particular interest about the novel SARS-CoV-2 (Table 4 ).

In recent years, a few epidrugs have been introduced into clinic use (e.g. vorinostat and belinostat mainly to treat haematological malignancies), and a wide range of epigeneticbased drugs are undergoing trials, which will clarify whether pharmacological epigenetic modulation is of clinical interest ( Table 5 ). The road from discovery to clinical approval requires long timelines; thus, the repurposing of old drugs interfering with epigenetic pathways is another goal. In this case, epigenetic effect is inevitably going to be 'off-target' in comparison with the drug action used in the first place. Experimental evidence demonstrated that the effects of epidrugs were achieved at lower doses with prolonged exposure, whereas higher drug concentrations were detrimental. However, when ongoing trials will be completed, we will establish clinically if the dose used for epigenetic modification reversal would be the same as, less than, or more than that used for the original purpose.

Curcumin Curcumin, belonging to the histone deacetylase inhibitor (HDACi) group, is a natural polyphenol extracted from turmeric with a wide range of molecular targets and drug activities, including anti-inflammatory properties. Interestingly, after H1N1 infection, curcumin treatment downregulated the secretion of proinflammatory cytokines and expression of the nuclear factor kappa-light-chain enhancer of activated B cell (NF-kB) gene in human macrophages without affecting cell viability. 93 This evidence suggests that curcumin may confer protection against influenza A virus-induced ALI by counteracting the cytokine signalling without damaging the immune system. 93 Interestingly, curcumin and demetoxycurcumin have been indicated as possible inhibitors of COVID-19 virus main protease, which plays a crucial function in controlling viral replication and transcription of SARS-CoV-2, suggesting a putative useful drugetarget interaction to be validated in clinical trials. 100 Apabetalone An international consortium of scientists has identified 50 proteins as putative drug targets against COVID-19. Amongst these targets, bromodomain (BRD) 2/4 would be relevant during interaction with the (E) envelope proteins of SARS-CoV-2 and viral reproduction. 94 By mimicking the histone structure, the (E) envelope proteins might potentially disrupt BRDhistone complexes. BRD proteins are epigenetic players that bind acetylated groups on histone proteins to aid in the recruitment of transcriptional machinery at promoter genes. Apabetalone can directly inhibit BET2/4 proteineSARS-CoV-2 interaction and may downregulate the expression of ACE2 receptors, which are exploited by the surface S glycoprotein to enter into human cells. 101 Currently, apabetalone is not approved by FDA, but has already shown clinical safety as demonstrated during the Phase 3 trial (BETonMACE) focusing on secondary prevention of cardiovascular dysfunction in diabetics. 102 Overall, this evidence suggests that apabetalone may potentially reduce viral infection and replication. In this way, Resverlogix Corporation (https://bit.ly/2CBaEKB) invites collaborators for further research on apabetalone as a putative therapeutic strategy for COVID-19.

Statins are hydroxymethylglutaryl-coenzyme A reductase inhibitors normalising lipid levels with pleiotropic epigeneticoriented effects by acting as HDACi. As statins also show anti-inflammatory effects, 103 they were thought to block the cytokine storm triggered by influenza viruses. 95 

Clinical evidence about the use of statins in the treatment of viral pneumonia is limited and provided mixed results. Indeed, two trials reported that the anti-inflammatory effects of statins may reduce cardiovascular risk and mortality in ICU patients affected by pneumonia. 109, 110 Otherwise, the results of one randomised clinical trial did not support statin use in those patients with ventilator-associated pneumonia. 111 Currently, there is no clinical or experimental evidence supporting the assertion that statins can improve clinical management of COVID-19. As the rates of acute events and mortality associated with COVID-19 infection are extremely high in patients with cardiovascular diseases (10.8%) and diabetics (7.3%), which generally use statins as primary or secondary prevention, these patients should continue the treatment when SARS-CoV-2 infection is suspected or diagnosed (https://www.acc.org/latest-in-cardiology/features/ /media/Non-Clinical/Files-PDFs-Excel-MS-Word-etc/2020/ 02/S20028-ACC-Clinical-Bulletin-Coronavirus.pdf). Statins are cleared by the liver metabolism and can increase the level of transaminases in cardio-hepatic patients 112 ; thus, strict evaluation and monitoring of statin therapy should be provided for COVID-19 patients, which commonly show an elevation of the aminotransferases (aspartate transaminase and alanine aminotransferase), with occasional alkaline phosphatase and total bilirubin elevations underlying a high risk for hepatotoxicity. 113, 114 Whether a de novo use of statin therapy may play a key role in preventing COVID-19 complications remains to be elucidated. Remarkably, experimental studies supported the hypothesis for which an early and high dose of statins might be a useful strategy for the treatment of MERS-CoV infections by directly affecting the TLReMYD88eNF-kB axis, which plays a pivotal role during CoV infections. 96, 115, 116 Statins are the most common FDA-approved drugs classified as TLReMYD88 antagonists; moreover, under normal conditions, statins did not strongly alter MYD88 levels, whereas they maintain basal MYD88 levels during stress and hypoxia. 96 This supports that statins might be protective for patients affected by COVID-19. Thus, the putative regulation of MYD88 pathway via statins may be an attractive field of research to explore how to protect innate immune response against novel viral respiratory infections, including SARS-CoV-2.

Metformin, belonging to HDACi class, is the first-line antihyperglycaemic drug for type 2 diabetes (T2D) patients, which can indirectly reduce chronic inflammation by normalising glucose levels or directly impact on inflammatory pathways. Recently, Saenwongsa and colleagues 117 have demonstrated that after the trivalent inactivated influenza vaccine (TIV), both the IgG antibody response and IFN-a expression were impaired in T2D patients treated with metformin via repression of rapamycin (mTOR)-mediated pathway and impaired IgG avidity index, leading to increased sensitiveness to H1N1 and H3N2 infection. This suggests that the TIV may not be suitable for T2D patients treated with metformin by emphasising the necessity of developing a more customised strategy for influenza prevention in high-risk groups. Metformin may recover the influenza vaccine responses in T2D patients (treated and non-treated with metformin) by improving the Bcell function via parallel downregulation of inflammation and upregulation of AMPK phosphorylation (active form), a metabolic enzyme involved also in antibody responses. 97 Understanding of the metformin effects on the immune system may guide the repurposing of this drug focused on therapeutic intervention on metabolism in inflammatory diseases.

Immunomodulators and antivirals: could they impact on epigenetic pathways underlying cardiovascular dysfunction in COVID-19?

The repurposing of both immunomodulators and antivirals, including tocilizumab (TCZ), remdesevir, favipiravir, hydroxychloroquine, and chloroquine, could be a fast way to get effective treatments whilst a preventive vaccine will be available (https://www.who.int/emergencies/diseases/novelcoronavirus-2019). In the current COVID-19 pandemic, TCZ is one of the most promising repurposed drugs under clinical investigation for the treatment of severe hospitalised pneumonia patients. Tocilizumab is a humanised monoclonal antibody that can counteract the cytokine storm by blocking the interleukin-6 (IL-6) receptor signalling associated with a high risk of cardiovascular mortality. 118 Immunomodulators can counteract the overactive inflammatory response, which seems to be the driver of increased disease severity. Many old anti-inflammatory drugs are in clinical trials, such as sarilumab (NCT04315298; Phases 2 and 3) and TCZ (NCT04320615; Phase 3). Besides, the efficacy of antivirals inhibiting viral replication, such as favipiravir (NCT04358549; Phase 2) and remdesevir (NCT04292730; Phase 3), is being evaluated in clinical trials compared with standard of care. The impact of COVID-19 on cardiovascular health is an urgent question for physicians. 119 As epigenetics plays an increasing role in cardiovascular diseases and inflammation, 102, 120 and also during SARS-CoV-2 infection, 77 we emphasised the need to clarify if these drugs could potentially impact the associated cardiac dysfunction modulating the severity of the disease.

Clinical evidence from rheumatoid arthritis patients demonstrated that TCZ therapy can prevent cardiovascular dysfunction via two main epigenetic-sensitive mechanisms: (i) reduction of NETosis; and (ii) upregulation of miRNA-23, miRNA-146, and miRNA-223 serum levels. 98 Overall, this suggests that TCZ can improve the pro-atherosclerotic status by regulating dyslipidaemias, endothelial dysfunction, inflammation, and oxidative stress. 98 Moreover, TCZ-treated rheumatoid arthritis patients demonstrated a differential expression of 85 lncRNAs in CD14 þ monocytes regulated by IL-6 or tumour necrosis factor-alpha. 99 Preliminary trials have suggested the usefulness of chloroquine or hydroxychloroquine repurposing in the treatment of COVID-19, which is correlated with the ability of these antimalarial agents in interfering with the cellular-mediated viral endocytosis. 121 However, a randomised trial demonstrated that hydroxychloroquine failed in preventing symptomatic infection when taken within 4 days after exposure. 122 At epigenetic level, hydroxychloroquine can exert an inhibitory activity against the polycomb repressive complex 2 (PRC2), responsible of switching chromatin towards a compacted state (inactive gene expression) in blood malignancies. 123 Interestingly, influenza A viruses, MERS-CoV, and SARS-CoV are able to activate the PRC2, which, in turn, increases the levels of H3K27me3 (repressive mark) at the promoters of targeted IFN-stimulated genes to counteract the host antiviral immune response. 124 This let us suggest that also SARS-CoV-2 might use the same mechanisms to inactive IFN-related pathways in infected cells; besides, since polycomb inhibitors have shown a general antiviral activity, 125 it might be useful to investigate whether hydroxychloroquine can directly impact on PRC2 activity in COVID-19. As reported, the clinical effect of i.v. remdesivir seems to be relatively modest; however, a randomised Phase 3 clinical trial (NCT04292899) did not find a significant difference in efficacy between 5-and 10-day courses of this drug. 126 Until now, there is no direct evidence that antivirals, such as remdesevir and favipiravir, would impact epigenetic-sensitive ways during their mechanism of action.

Targeted epigenetic-sensitive molecular networks are temporally manipulated during virusehost interactions, providing further risk factors for viral shedding and inadequate immune response also in patients affected by COVID-19, in which ACE2 promoter hypomethylation may be one of the relevant drivers. During the current COVID-19 pandemic, we need to understand why a part of the population becomes critically infected when exposed to low viral load, whilst other subjects are less responsive when exposed to high viral loads. As the influenza virus may also promote acute coronary syndromes (which can be reduced by vaccine), 127 the issue of coinfection (i.e. SARS-CoV-2 and influenza viruses) needs to be further explored both in terms of epigenetic-sensitive tandem events and in critical care. For better risk stratification, it would be needed to clarify the SARS-CoV-2 basic mechanisms of action and how these impact on the individual genetic/ epigenetic background and pre-existent cardio-metabolic diseases highly correlated with mortality rate, especially in the elderly. 128, 129 Clinical treatment of mild forms of COVID-19 should not be phobic from fever, which can promote an effective immune response and virus clearance from the body. 130 Ongoing controlled clinical trials would clarify the repositioning of TCZ, whereas curcumin, apabetalone, metformin, and statins could be an effective treatment to protect innate immune response against severe viral respiratory infections. In the era of network medicine, predictive analysis tools are playing a relevant role in addressing the COVID-19 pandemic by providing maps of human proteins interacting with SARS-CoV-2 proteins 101 and a list of candidate repurpose drugs and potential drug combinations targeting SARS-CoV-2. 131 The epigenetic susceptibility to pulmonary viral infections requires further investigation by using the network-oriented analysis to clarify the molecular routes underlying perturbation of the human interactome, 132 in particular in COVID-19 and its impact on cardiovascular health.

Epidemiology of 2009 pandemic influenza A (H1N1) in the United States

Epidemiology of human infections with avian influenza A(H7N9) virus in China

SARS and MERS: recent insights into emerging coronaviruses

Another decade, another coronavirus

A novel coronavirus from patients with pneumonia in China

Lung pathology of fatal severe acute respiratory syndrome

Emerging respiratory infections: the infectious disease pathology of SARS, MERS, pandemic influenza, and Legionella

Organ distribution of severe acute respiratory syndrome (SARS) associated coronavirus (SARS-CoV) in SARS patients: implications for pathogenesis and virus transmission pathways

Into the eye of the cytokine storm

The inflammatory response triggered by Influenza virus: a two edged sword

Coronavirus infections and immune responses

Sch€ afer A, Baric RS. Epigenetic landscape during coronavirus infection

Epigenetic control of immunity

Epigenetics mechanisms in multiorgan dysfunction syndrome

Clinical epigenetics and multidrug-resistant bacterial infections: host remodelling in critical illness

Antagonism of dsRNA-induced innate immune pathways by NS4a and NS4b accessory proteins during MERS coronavirus infection

Pathogenic influenza viruses and coronaviruses utilize similar and contrasting approaches to control interferon-stimulated gene responses

Suppression of the antiviral response by an influenza histone mimic

Structural basis for histone mimicry and hijacking of host proteins by influenza virus protein NS1

The miRNA complexes against coronaviruses COVID-19

Implications of the virusencoded miRNA and host miRNA in the pathogenicity of SARS-CoV-2. arXiv 2020. Advance Access published on

Epigenetic coordination of acute systemic inflammation: potential therapeutic targets

Epigeneticsensitive pathways in personalized therapy of major cardiovascular diseases

Zoonotic infections with avian influenza A viruses and vaccine preparedness: a game of mix and match

Human influenza A H5N1 virus related to a highly pathogenic avian influenza virus

Avian influenza A (H5N1) infection in humans

Writing Committee of the Second World Health Organization Consultation on Clinical Aspects of Human Infection with Avian Influenza A (H5N1) Virus

Critically ill patients with 2009 influenza A(H1N1) in Mexico

Emergence of a novel swine-origin influenza A (H1N1) virus in humans

Hospitalized patients with 2009 H1N1 influenza in the United States

Critically ill patients with 2009 influenza A(H1N1) infection in Canada

Critical care services and 2009 H1N1 influenza in Australia and New Zealand

Influenza A (H1N1pdm09)-related critical illness and mortality in Mexico and Canada

Influenza viruses and cross-reactivity in healthy adults: humoral and cellular immunity induced by seasonal 2007/2008 influenza vaccination against vaccine antigens and 2009 A(H1N1) pandemic influenza virus

Pathology of fatal human infection associated with avian influenza A H5N1 virus

Re-emergence of fatal human influenza A subtype H5N1 disease

Lung pathology in fatal novel human influenza A (H1N1) infection

Pandemic influenza A (H1N1): pathology and pathogenesis of 100 fatal cases in the United States

Cytokine and chemokine profiles in lung tissues from fatal cases of 2009 pandemic influenza A (H1N1): role of the host immune response in pathogenesis

Immune responses in influenza A virus and human coronavirus infections: an ongoing battle between the virus and host

The cytokine storm of severe influenza and development of immunomodulatory therapy

Spectrum of clinical and radiographic findings in patients with diagnosis of H1N1 and correlation with clinical severity

Fatal outcome of human influenza A (H5N1) is associated with high viral load and hypercytokinemia

Origin and evolution of pathogenic coronaviruses

Genomic characterisation and epidemiology of 2019 novel coronavirus: implications for virus origins and receptor binding

Overlapping and discrete aspects of the pathology and pathogenesis of the emerging human pathogenic coronaviruses SARS-CoV, MERS-CoV, and 2019-nCoV

The epidemic of 2019-novelcoronavirus (2019-nCoV) pneumonia and insights for emerging infectious diseases in the future

SARS and other coronaviruses as causes of pneumonia

Middle East respiratory syndrome coronavirus: risk factors and determinants of primary, household, and nosocomial transmission

Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China

Epidemiological and clinical characteristics of 99 cases of 2019 novel coronavirus pneumonia in Wuhan, China: a descriptive study

Clinical characteristics of coronavirus disease 2019 in China

Presenting characteristics, comorbidities, and outcomes among 5700 patients hospitalized with COVID-19 in the New York City area

Cardiovascular disease, drug therapy, and mortality in Covid-19

Baseline characteristics and outcomes of 1591 patients infected with SARS-CoV-2 admitted to ICUs of the Lombardy region

Clinical characteristics of 113 deceased patients with coronavirus disease 2019: retrospective study

Radiological findings from 81 patients with COVID-19 pneumonia in Wuhan, China: a descriptive study

Pathological study of the 2019 novel coronavirus disease (COVID-19) through postmortem core biopsies

Clinicopathologic, immunohistochemical, and ultrastructural findings of a fatal case of Middle East respiratory syndrome coronavirus infection in the United Arab Emirates

Multiple organ infection and the pathogenesis of SARS

Angiotensin-converting enzyme 2 (ACE2) as a SARS-CoV-2 receptor: molecular mechanisms and potential therapeutic target

Cell entry mechanisms of SARS-CoV-2

Dipeptidyl peptidase 4 distribution in the human respiratory tract: implications for the Middle East respiratory syndrome

Cryo-EM structure of the 2019-nCoV spike in the prefusion conformation

The spike glycoprotein of the new coronavirus 2019-nCoV contains a furin-like cleavage site absent in CoV of the same clade

Angiotensin-converting enzyme 2 protects from severe acute lung failure

A crucial role of angiotensin converting enzyme 2 (ACE2) in SARS coronavirusinduced lung injury

DPP4, the Middle East respiratory syndrome coronavirus receptor, is upregulated in lungs of smokers and chronic obstructive pulmonary disease patients

Cell host response to infection with novel human coronavirus EMC predicts potential antivirals and important differences with SARS coronavirus

Distinct immune response in two MERS-CoV-infected patients: can we go from bench to bedside?

An update on current therapeutic drugs treating COVID-19

Epigenetics of hostepathogen interactions: the road ahead and the road behind

Early local immune defences in the respiratory tract

Antiviral B cell and T cell immunity in the lungs

H5N1 influenza virus-specific miRNA-like small RNA increases cytokine production and mouse mortality via targeting poly(rC)-binding protein 2

Epigenetic dysregulation of ACE2 and interferon-regulated genes might suggest increased COVID-19 susceptibility and severity in lupus patients

Targeting potential drivers of COVID-19: neutrophil extracellular traps

Engineered RNA viral synthesis of microRNAs

Influenza A virus expresses high levels of an unusual class of small viral leader RNAs in infected cells

tenOever BR. RNA viruses and the host microRNA machinery

Comparative replication and immune activation profiles of SARS-CoV-2 and SARS-CoV in human lungs: an ex vivo study with implications for the pathogenesis of COVID-19

DNA methylation analysis of the COVID-19 host cell receptor, angiotensin I converting enzyme 2 gene (ACE2) in the respiratory system reveal age and gender differences

Pulmonary embolism or pulmonary thrombosis in COVID-19? Is the recommendation to use high-dose heparin for thromboprophylaxis justified?

Interplay between genetics and epigenetics in modulating the risk of venous thromboembolism: a new challenge for personalized therapy

Neutrophil extracellular traps are elevated in patients with pneumonia-related acute respiratory distress syndrome

Anticoagulant treatment is associated with decreased mortality in severe coronavirus disease 2019 patients with coagulopathy

Harnessing innate immunity to eliminate SARS-CoV-2 and ameliorate COVID-19 disease

The architecture of SARS-CoV-2 transcriptome

Control of viral infections by epigenetic-targeted therapy

Epigenetic mechanisms of importance for drug treatment

Curcumin alleviates macrophage activation and lung inflammation induced by influenza virus infection through inhibiting the NF-kB signaling pathway. Influenza Other Respir Virus

A SARS-CoV-2 protein interaction map reveals targets for drug repurposing

Simvastatin suppresses RANTES-mediated neutrophilia in polyinosinicepolycytidylic acid-induced pneumonia

Statins may decrease the fatality rate of Middle East respiratory syndrome infection

Metformin improves in vivo and in vitro B cell function in individuals with obesity and type-2 diabetes

Tocilizumab improves the proatherothrombotic profile of rheumatoid arthritis patients modulating endothelial dysfunction, NETosis, and inflammation

Interleukin-6 and tumour necrosis factor-a differentially regulate lincRNA transcripts in cells of the innate immune system in vivo in human subjects with rheumatoid arthritis

Potential inhibitor of COVID-19 main protease (M pro ) from several medicinal plant compounds by molecular docking study

Structural basis for the recognition of SARS-CoV-2 by full-length human ACE2

Differential epigenetic factors in the prediction of cardiovascular risk in diabetic patients

Influence of statins on influenza vaccine response in elderly individuals

Mechanisms of action and efficacy of statins against influenza

Impact of statins on influenza vaccine effectiveness against medically attended acute respiratory illness

Effect of statin use on influenza vaccine effectiveness

Statin use and risks of influenza-related outcomes among older adults receiving standard-dose or high-dose influenza vaccines through Medicare during

Efficacy of high-dose versus standard-dose influenza vaccine in older adults

Effect of pravastatin on the frequency of ventilator-associated pneumonia and on intensive care unit mortality: openlabel, randomized study

Effect of statin treatment on short term mortality after pneumonia episode: cohort study

Effect of statin therapy on mortality in patients with ventilatorassociated pneumonia: a randomized clinical trial

Epigenetic-sensitive challenges of cardio-hepatic interactions: clinical and therapeutic implications in heart failure patients

Clinical features of COVID-19-related liver damage

Liver injury during highly pathogenic human coronavirus infections

Effects of simvastatin on cell viability and proinflammatory pathways in lung adenocarcinoma cells exposed to hydrogen peroxide

Atorvastatin attenuates myocardial remodeling induced by chronic intermittent hypoxia in rats: partly involvement of TLR-4/MYD88 pathway

Metformin-induced suppression of IFN-a via mTORC1 signalling following seasonal vaccination is associated with impaired antibody responses in type 2 diabetes

Relationship between interleukin 6 and mortality in patients with unstable coronary artery disease: effects of an early invasive or noninvasive strategy

Coronavirus disease 2019 (COVID-19) and cardiovascular disease

Precision medicine in distinct heart failure phenotypes: focus on clinical epigenetics

New insights on the antiviral effects of chloroquine against coronavirus: what to expect for COVID-19?

A randomized trial of hydroxychloroquine as postexposure prophylaxis for Covid-19

A drug repurposing screening reveals a novel epigenetic activity of hydroxychloroquine

Targeting SARS-CoV-2 using polycomb inhibitors as antiviral agents

Inhibitors of the histone methyltransferases EZH2/1 induce a potent antiviral state and suppress infection by diverse viral pathogens

Remdesivir for 5 or 10 days in patients with severe Covid-19

Influenza vaccination reduces cardiovascular events in patients with acute coronary syndrome

Cardiovascular involvement during COVID-19 and clinical implications in elderly patients. A Review

Can COVID 2019 disease induce a specific cardiovascular damage or it exacerbates pre-existing cardiovascular diseases?

COVID-19: do not be phobic from fever

Network-based drug repurposing for novel coronavirus 2019-nCoV/SARS-CoV-2

Molecular networks in network medicine: development and applications

This research was supported (in whole or in part) by Hospital Corporation of America (HCA) or HCA affiliated entity. The views expressed in this publication represent those of the authors and do not necessarily represent the official views of HCA or any of its affiliated entities.

Design/implementation of the review: EC, GB, CN Critical feedback: NF-M, MG Writing of paper: all authors

The authors declare that they have no conflicts of interest.