[Glycocalyx Awareness! Part 3] From SARS-infection to COVID

Extensive reading recommendations on SARS-CoV-2/ COVID: all mechanisms involved (Part 2)

Mechanisms involved in SARS-CoV-2 / COVID-19

It has been clear since the SARS epidemic of 2003 that coronavirus diseases caused by SARS-CoV infections are thromboinflammatory diseases. As of March 2020, when SARS-CoV-2 was politically (finally) declared a pandemic, COVID-19 was still treated like a main pulmonary disease. Reseachers have been pointing out that the underlying mechanisms are characterized by hyperinflammation, hypercoagulation, complement cascades and dysregulation of the Renin-Angiotensin-Aldosterone System, ultimately leading to thromboembolic events in multiple organs (MOF), stroke and post-COVID systemic diseases, such as Guillain-Barré and cardiomyopathy. 

To provide a view into the complexity of COVID-19, I share with you the most prominent research papers on the mechanisms and pathogenicity of SARS-CoV-2. Some of the research papers of the biggest relevance for COVID-19 complications are as old as 60 years. This is why the paradigm should be that "Lots of the mechanisms causing COVID-19 are well-known, but we have to find the best practices to treat its complications".

I only refer to verified and reviewed research and scientific viewpoint papers citing verified references. If paper has already been peer reviewed but still awaitens the editory process (early release), I will mention this. To retrieve these papers from the PubMed/NCBI and Wiley database, I narrowed my search process to combinations of "SARS-CoV-2", "Thrombosis", "Pulmonary embolism", "Complement" and "Coagulation".

ACE and ACE2
Angiotensin Converting Enzyme defects in shock: implications for future therapy, Critical Care 22, Art. No. 274 (2018);

ADAM17
TMPRSS2 and ADAM17 Cleave ACE2 Differentially and Only Proteolysis by TMPRSS2 Augments Entry Driven by the SARS-Coronavirus Spike Protein, Journal of Virology, January 2014 Vol. 88, No. 2, P1293-1307;

Aquaporins
Aquaporin-mediated transport, Pathway R-HSA-445717, PubChem, 08 July 2020;

ARDS
Radiological findings from 81 patients with COVID-19 pneumonia in Wuhan, China: a descriptive study, Lancet Infectious Diseases Vol. 20, Issue 4, P425-434;
The evolving role of the Renin-angiotensin system in ARDS, Critical Care 21, Art. No. 329 (2017);

Asymptomatic SARS-CoV-2 Infection
Natural History of Asymptomatic SARS-CoV-2 Infection, NEJM 2020; 383:885-886, August 27, 2020;

B- and T-cell immunological memory (CD4+ and CD8+)
COVID-19 and the Path to Immunity, JAMA, September 11, 2020;
Depletion of CD4 and CD8 Positive T Cells Impairs Venous Thrombus Resolution in Mice, MDPI International Journal of Molecular Sciences 2020 March;21(5): 1650;

Call for better screening
Pathophysiological Basis and Rationale for Early Outpatient Treatment of SARS-CoV-2 (COVID-19) Infection, The American Journal of Medicine, August 06, 2020;

Cardiovascular complications
Outcomes of Cardiovascular MRI in Patients Recently Recovered from COVID-19 (coronavirus causes myocardial inflammation independent of preexisting conditions), JAMA Cardiology, July 27, 2020;

Coagulation
Immunothrombotic Dysregulation in COVID-19 Pneumonia is Associated with Respiratory Failure and Coagulopathy, Journal of Circulation, 28 July 2020;
Coagulation biomarkers are independent predictors of increased oxygen requirements in COVID-19, Journal of Thrombosis and Haemostasis, 17 August 2020;
Coagulation parameters and venous thromboembolism in patients with and without COVID-19 admitted to the Emergency Department for acute respiratory insufficiency, Thrombosis Research Vol. 196, P209-212, December 2020;

Complement
Association of COVID-19 inflammation with activation of the C5a-C5aR1 axis, Nature 2020, 29 July 2020;
COVID-19: A collision of complement, coagulation and inflammatory pathways, Journal of Thrombosis and Haemostasis Vol. 18, Issue 9, September 2020, P2110-2117;

Comparative tropism and transmission (profiling of SARS-CoV-2)
Distinct conformational states of SARS-CoV-2 Spike protein, Science 21 July 2020;
Coronavirus surprise from cryo-EM data, Wiley Analytical Science, 22 July 2020;
Single-Cell Sequencing of Peripheral Mononuclear Cells Reveals Distinct Immune Response Landscapes of COVID-19 and Influenza Patients, Immunity Vol. 53, Issue 3, 15 September 2020, P685-696;
Enhanced Binding of SARS-CoV-2 Spike Protein Receptor by Distal Polybasic Cleavage Site, ACS Nano 2020, 14, 8, 10616-10623;
Enhanced receptor binding of SARS-CoV-2 through networks of hydrogen-bonding and hydrophobic interactions, Proceedings of the National Academy of Sciences of the US (PNAS) June 23, 2020 117 (25), 13967-13974;
Pathogenicity, Transmission, Diagnosis and Treatment of COVID-19, JAMA 2020;324(8):782-793;
Risk of Ischemic Strole in Patients with COVID-19 vs. Patients With Influenza, JAMA Neurology, July 2, 2020;

Central Nervous System (CNS) complications
A case of malignant cerebral infarction associated with COVID-19 infection, British Journal of Neurosurgery, 05 August 2020;

Critical Care
Association of Noninvasive Oxygenation Strategies with All-Cause Mortality in Adults with Acute Hypoxemic Respiratory Failure: A Systematic Review and Analysis, JAMA 2020;324(1):57-67;
Anti Xa activity after high dose Low Molecular Weight Heparin (LMWH) thrombosis prophypaxis in COVID-19 patients at the IC Unit, Thrombosis Research Vol. 196, P1-3, December 01, 2020;
Impact of implementation of an individualised thromboprophylaxis protocol in critically ill ICU patients with COVID-19: A longitudinal controlled before and after study, Thrombosis Research Vol. 194, October 2020, P209-215;
Scientific and Standardization Committee communication: Clinical guidance on the diagnosis, prevention and treatment of Venous Thromboembolism (VTE) in hospitalized patients with COVID-19, Journal of Thrombosis and Haemostasis Vol. 18, Issue 8, August 2020, P1859-1865;
Inaccuracy of point-of-care international normalized ratio in Rivaroxaban-treated patients, Annals of Pharmacotherapy Vol. 47, Issue 9, September 1, 2013;
How I treat recurrent Venous Thromboembolism in patients receiving anticoagulant therapy, Blood Vol. 129, Issue 25, June 22, 2017;

Deep Vein Thrombosis (DVT)
Deep vein thrombosis in SARS-CoV-2 pneumonia-affected patients within standard care units: Exploring a submerged portion of the iceberg, Thrombosis Research Vol. 194, October 2020, P216-219;
Incidence of deep vein thrombosis among non-ICU patients hospitalized for COVID-19 despite pharmacological thromboprophylaxis, Journal of Thrombosis and Haemostasis Vol. 18, Issue 9, September 2020;

DIC (Disseminated Intravascular Coagulopathy) and differentiations of DIC
Clotting abnormalities in critically ill COVID-19 patients are inconsistent with overt Disseminated Intravascular Coagulation, Thrombosis Research Vol. 196, P272-275, December 01, 2020;
Higher procoagulatory potential but lower DIC score in COVID-19 ARDS patients compared to non-COVID-19 ARDS patients, Thrombosis Research Vol. 196, P186-192, December 01, 2020;

Endothelialitis/Endotheliitis
Pulmonary Vascular Endothelialitis, Thrombosis and Angiogenesis in COVID-19, New England Journal of Medicine (NEJM) 2020; 383:120-128, July 9, 2020;

Fibrinolysis
Fibrinolytic abnormalities in ARDS and versatility of thrombolytic drugs to treat COVID-19, Journal of Thrombosis and Haemostasis Vol. 18, Issue 7, July 2020;
Hypofibrinolytic state and high thrombin generation may play a major role in SARS-CoV-2 associated thrombosis, Journal of Thrombosis and Haemostasis Vol. 18, Issue 9, September 2020;

Interferons (IFN)
Role of IFN-γ responsiveness in CD8 T cell-mediated viral clearance and demyelination in coronavirus-infected mice, Journal of Neuroimmunology 2008 February; 194(1): 18-26;
Type I and Type III Interferons- Induction, Signaling, Evasion and Application to combat COVID-19, Cell Host & Microbe Vol. 27, Issue 6, p870-878, June 10, 2020;

Megakaryocytes
Megakaryocytes and platelet-fibrin thrombi characterize multi-organ thrombosis at autopsy in COVID-19: A case series, EClinicalMedicine Vol. 24, 100434, July 01, 2020;

Monocytes
Monocyte activation in systemic COVID-19 infection: Assay and rationale, EBioMedicine Vol. 59, 102964, September 01, 2020;

Neutrophils and NETs (& platelet interaction)
Immunothrombosis in severe COVID-19, EBioMedicine Vol. 59, 102942, September 01, 2020;

Pathogenicity of SARS-CoV-2: PROS1 and PL proteins
Identification of the antithrombotic protein S as a potential target of the SARS-CoV-2 palpain-like protease, Thrombosis Research Vol. 196, P257-259, December 01, 2020;

Pathogenicity of SARS-CoV-2: RNA and Spike protein
Circulating endothelial progenitors are increased in COVID-19 patients and correlate with SARS-CoV-2 RNA in severe cases, Journal of Thrombosis and Haemostasis, 06 August 2020;
Cleavage of spike protein of SARS coronavirus by protease factor Xa is associated with viral infectivity, Biochemical and Biophysical Research Communications 2007, July 20; 359(1): 174-179;

Platelets
Intravascular Platelet Aggregation in the Heart Induced by Norepinephrine, Journal of Circulation, 1972;46:698-708;
Platelet protein S limits venous but not arterial thrombosis propensity by controlling coagulation in the thrombus, Blood Vol. 135, Issue 22, May 28, 2020;

Pulmonary Embolism
Subsegmental Thrombus in COVID-19 Pneumonia: Immunothrombosis or Pulmonary Embolism? Data Analysis of Hospitalized Patients with Coronavirus Disease, Heart, Lung and Circulation, 24 August 2020;
Late Pulmonary Embolism after COVID-19 Pneumonia Despite Adequate Rivaroxaban Treatment, European Journal of Case Reports in Internal Medicine Vol. 7, No. 7, June 18, 2020;

Pyroptosis
Inflammasomes and Pyroptosis as Therapeutic Targets for COVID-19, The Journal of Immunology Vol. 205, Issue 2, 15 July 2020, P307-312;

RAAS (Renin-Angiotensin-Aldosterone) - KKS (Kallikrein-Kinin), Angiotensins and Bradykinin
Involvement of bradykinin B1 and B2 receptors in human PMN elastase release and increase in endothelial cell monolayer permeability, Immunopharmacology, 1996 June;33(1-3):325-9;
The Renin-Angiotensin System: An integrated view of lung disease and coagulopathy in COVID-19 and therapeutic implications, Journal of Experimental Medicine (2020) 217 (8):e20201000;
The evolving role of the Renin-angiotensin system in ARDS, Critical Care 21, Art. No. 329 (2017);

Stroke (and prevalence in young people due to SARS-CoV-2 infection)
Acute cerebral stroke with multiple infarctions and COVID-19, France, 2020, CDC Research Vol. 26, No. 9, September 2020;
A case of malignant cerebral infarction associated with COVID-19 infection, British Journal of Neurosurgery, 05 August 2020;
COVID-19 related stroke in young individuals, Lancet Neurology Vol. 19, Issue 9, P713-715, September 01, 2020;
Risk of Ischemic Strole in Patients with COVID-19 vs. Patients With Influenza, JAMA Neurology, July 2, 2020;
Stroke as a complication and prognostic factor of COVID-19, Neurologia Vol. 35, Issue 5, June 2020, P318-322;
Mechanisms of Stroke in COVID-19, Cerebrovascular Diseases Vol. 49, No. 4,  September 2020;

Systemic diseases following SARS-CoV-2 infection
Autoimmune and inflammatory diseases following COVID-19, Nature Reviews Rheumatology 16, 413-414(2020);

Thrombosis
Arterial Mesentric Thrombosis as a Complication of SARS-CoV-2 Infection, European Journal of Case Reports in Internal Medicine 2020; 7(5): 001690;
Multisystemic Infarctions in COVID-19: Focus on the Spleen, European Journal of Case Reports in Internal Medicine 2020; 7(7): 001747;
Clotting abnormalities in critically ill COVID-19 patients are inconsistent with overt Disseminated Intravascular Coagulation, Thrombosis Research Vol. 196, P272-275, December 01, 2020;
Asymptomatic Deep Vein Thrombosis (DVT) in critically ill COVID-19 patients despite therapeutic levels of anti-Xa activity, Thrombosis Research Vol. 196, P268-271, December 01, 2020;
Extensive pulmonary perfusion defects compatible with microthrombosis and thromboembolic disease in severe COVID-19 pneumonia, Thrombosis Research Vol. 196, P135-137, December 01, 2020;
Systemic thromboemboli in patients with COVID-19 may result from paradoxical embolization, Thrombosis Research Vol. 196, P206-208, December 01, 2020;
Circulating endothelial progenitors are increased in COVID-19 patients and correlate with SARS-CoV-2 RNA in severe cases, Journal of Thrombosis and Haemostasis, 06 August 2020;
Thromboembolic events and apparent heparin resistance in patients infected with SARS-CoV-2, International Journal of Laboratory Hematology 2020 June;42:19-20;

Treatment/therapeutic options for treating COVID
Treatment of patients with acute Deep Vein Thrombosis and/or pulmonary embolism: efficacy and safety of non-VKA oral anti-coagulants in selected populations, Thrombosis Research Vol. 134, Issue 2, p227-233, August 01, 2014;
Ig-like ACE2 protein therapeutics: a revival in development during a pandemic, Journal of mAbs (antibodies) Vol. 12, Issue 1, December 2020;
Therapeutic blockade of granulocyte macrophage colony-stimulating factor (GM-CSF) in COVID-19 associated hyperinflammation: challenges and opportunities, Lancet Respiratory Medicine Vol. 8, Issue 8, p822-830, August 2020;
Fibrinolytic abnormalities in ARDS and versatility of thrombolytic drugs to treat COVID-19, Journal of Thrombosis and Haemostasis Vol. 18, Issue 7, July 2020;
Dynamic changes in fibrinogen and D-dimer levels in COVID-19 patients on nafamostat mesylate, Journal of Thrombosis and Thrombolysis 2020, 12 September 2020 (note: trial from Tokyo Hospital, coagulation dynamics might differ in non-Asian people);
Kallikrein-kinin blockade in patients with COVID-19 to prevent ARDS, Radboud UMC, April 27, 2020;
Accumulating evidence suggests anti-TNF therapy needs to be given trial priority in COVID-19 treatment, Lancet Rheumatology, September 04, 2020;
GM-CSF Blockade during Chimeric Antigen Receptor T Cell Therapy Reduces Cytokine Release Syndrome and Neurotoxicity and May Enhance Their Effector Functions, ASH Blood Vol. 132, November 29, 2018;
GM-CSF Neutralization With Lenzilumab in Severe COVID-19 Pneumonia: A Case-Control Study, Mayo Clinic Proceedings, 03 September 2020;
Effect of Dexamethasone on Days Alive and Ventilator-Free in Patients With Moderate or Severe ARDS and COVID-19: the CoDEX Randomized Clinical Trial, JAMA, September 2, 2020;
Effect of Hydrocortisone Among Critically Ill Patients With COVID-19: A Randomized Clinial Trial, JAMA, September 2, 2020;
The Role of Anticoagulation in COVID-19 Induced Hypercoagulability, Current Cardiology Reports 22, Art. No. 53(2020);

Viral load and antibody responses
Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study, Lancet Infectious Diseases Vol. 20, Issue 5, P565-574;

SARS-CoV-2: is aanpassing van ACE2 binnen het RAAS een therapeutische optie?

Dit bericht is de Nederlandse versie van mijn bericht van 18 april 2020: "Pathways to deterioration in SARS-CoV-2: is enhancement of ACE2 in the RAAS system key? 
Het is bekend dat de spike-glycoproteïne (S) van SARS-CoV-2 humaan Angiotensineconverterend enzym 2-receptoren (ACE2-receptoren) gebruikt om de cellen van de gastheer binnen te dringen. De ACE2-receptor wordt aangetroffen in type II alveolaire cellen (AT2) van de longen, slokdarmepitheelcellen, enterocyten uit ileum en colon, neusholte, vasculaire endothelia, nierweefsel, epithelia van de dunne darm, testes en op de epitheelcellen van mondslijmvlies (High expression of ACE2 receptor of 2019-nCoV on the epithelial cells of oral mucosa, International Journal of Oral Science, 24 February 2020 ), evenals in de hersenstam en neurale cortex. SARS valt ACE2-verrijkte cellen binnen, alleen om zichzelf zeer snel te repliceren om andere cellen te samentrekken. Van de infectie van type II-pneumocyten en het vrijkomen van virussen in de luchtwegen met de nabijheid van het pulmonale capillaire bed wordt sterk vermoed dat het systemische verspreiding van het virus naar andere organen mogelijk maakt (ACE2 Receptor Expression and SARS Infection Depend on Differentiation of Human Airway Epithelia, Journal of Virology, December 2005).

Is ARDS een adequate classificatie?
Het is nog onduidelijk wat precies de plotse achteruitgang is bij ernstig zieke SARS-CoV-2-patiënten. Een plotselinge verslechtering bij patiënten met zuurstoftekort wordt aangeduid als "Acute Respiratory Distress Syndrome" (ARDS). Het valt te betwijfelen of ARDS, gekenmerkt door bilaterale infiltraten, hypoxemie en kortademigheid (Acute Lung Injury and ARDS: Pathophysiology and Treatment, Missouri Medicine, Jul-Aug 2010), een geschikte classificatie is voor de pathofysiologie geassocieerd met SARS-CoV-2 (COVID-19 Pneumonia: ARDS or not?, Critical Care 24, Article number 154 (2020)). Over het algemeen wordt de rol van specifieke pathogenen voor de ontwikkeling van ARDS als moeilijk te beoordelen beschouwd (Acute Respiratory Distress Syndrome and Pneumonia: A Comprehensive Review of Clinical Data, Clinical Infectious Diseases, Vol. 43 Issue 6, 15 September 2006.

Pathologische bevindingen van een vroege COVID-casestudy: overactivering van T-cellen
In één geval met betrekking tot pathologische bevindingen van COVID-19 geassocieerd met ARDS, bleef de zuurstofverzadiging boven de 95% tot de veertiende ziektedag. Op dag 14 van de ziekte verslechterde de hypoxemie en daalde de zuurstofsaturatie tot onder de 60%, gevolgd door een hartstilstand. Bilaterale diffuse alveolaire schade met cellulaire fibromyxoïde exsudaten (wondvocht) werd waargenomen, evenals een toename van pneumocyten en hyaline membraanvorming in de rechterlong; de linkerlong vertoonde longoedeem met hyalinevorming. Deze bevindingen werden beschouwd als suggestief voor ARDS met vroege aanvang. In beide longen werden mononucleaire inflammatoire infiltraten waargenomen die gedomineerd werden door lymfocyten. 

Een van de belangrijkste bijdragen tot verslechtering in dit geval was waarschijnlijk een overactivering van T-cellen. Hoewel perifere CD4- en CD8-T-cellen waren verminderd, waren ze hyperactief. Grote hoeveelheden HLA-DR (die antigeen presenteren en een ligand aan T-cellen leveren) en CD38 (glycoproteïne op het oppervlak van immuuncellen) werden gezien. Concentraties van CCR6 + Th17 (T-helpercellen) waren hoog, CD8 T-cellen bleken hoge concentraties cytotoxische granulaten te bevatten (Pathological findings of COVID-19 associated with ARDS, The Lancet, February 18 2020). Soortgelijke observaties werden gedaan in een onderzoek uit 2005 (ACE2 Receptor Expression and SARS Infection Depend on Differentiation of Human Airway Epithelia, Journal of Virology, December 2005).

Cytokine storm en invasie van het centrale zenuwstelsel en een rol voor Tocilizumab
Cytokine-storm, een overreactie van het immuunsysteem van de gastheren, is geopperd om de mechanismen achter plotselinge verslechtering te verklaren (The cytokine release syndrome of severe COVID-19 and IL-6R antagonist Tocilizumab may be the key, International Journal of Antimicrobial Agents, 29 March 2020; zie ook Cytokine release syndrome in severe COVID-19, AAAS, 17 April 2020); zie ook Cytokine release syndrome bij ernstige COVID-19, AAAS, 17 april 2020). Een andere route zou de invasie van het centrale zenuwstelsel en de hersenstam kunnen zijn, wat het zuurstofgebrek van patiënten zou kunnen verklaren. Beide routes zijn onlangs door onderzoekers afgewezen, omdat de verstrekte gegevens nog steeds onvoldoende zijn om te bewijzen dat ofwel cytokinestorm ofwel betrokkenheid van het CZS een belangrijke rol speelt bij zuurstofgebrek - naast meervoudig orgaanfalen.

Multi-factor beoordeling
Allereerst moet worden opgemerkt dat er geen homogeen soort ARDS bestaat. ARDS is een definitie die het acute begin van hypoxemie beschrijft (ARDS subphenotypes: Understanding a heterogeneous syndrome, Critical Care, 24 March 2020). Evenzo is de immuniteitsrespons bij SARS-CoV-2-patiënten heterogeen: behandeling van immuniteitsrespons is geen 'one size fits all'-zaak. Dit wordt nog verder bemoeilijkt door het feit dat immunomodulatie de antivirale activiteit in de gastheer niet mag schaden.

Wat moet en kan worden geleerd van SARS-1 (2003) als het gaat om het beoordelen van medische factoren?
Een uitgebreide beoordeling met meerdere factoren kan nuttig zijn om de routes van SARS, van invasie tot achteruitgang, te verklaren. Het lichaam is een systeem waarin de aangetaste delen elk bijdragen aan de ernst van de ziekte. Immuniteit en cardiovasculaire mechanismen zijn met elkaar verweven, daarom kan niet worden aangenomen dat deze mechanismen onafhankelijk bijdragen aan verslechtering. Deze systemen zijn een basisbehoefte om de machine draaiende te houden. Ik zou zeggen dat SARS in hoofdzaak een onbalans in de homeostase veroorzaakt, gekenmerkt door ACE2-verstoring en onbalans van het Renine-Angiotensine-Aldosteronsysteem, schade aan endotheelweefsel, hetgeen aanzet tot de ontstekingssoep / cascade, trombotische gebeurtenissen - deze mechanismen versterken elkaar in een overdrive-modus. Het samenspel tussen ontsteking en veneuze trombo-embolie is niet alleen een oorzaak en gevolg, maar een verweven interactie. Zie bijvoorbeeld: ''The role of inflammation in Venous Thromboembolism', Frontiers in Pediatrics, 23 May 2018, 2018:6:142'. 

Wat SARS-CoV-1 duidelijk heeft gemaakt, is dat stollingsstoornissen vaak voorkomen in ernstige gevallen. Endotheliumbeschadiging kan een vroege oorzaak zijn van een ontstekingscascade, gevolgd door trombotische voorvallen. In een SARS-recensie uit 2004 werd gezegd dat de SARS-epidemie-ervaring van 2003 een verhoogde waakzaamheid tegen beroerte en andere trombotische SARS-gerelateerde gebeurtenissen zou moeten rechtvaardigen bij toekomstige uitbraken van coronavirussen (Large artery ischaemic stroke in SARS, Journal of Neurology 251, October 2004).

Ik kom bij wat me intrigeerde in het kader van andere ziektestudies (cardiovasculair) en wat mijn aandacht weer trok tijdens de vroege fase van de SARS-CoV-2-pandemie: dat is de plausibele rol van ACE2 als onderdeel van het RAAS-systeem en het nadelige verlies van ACE2 tijdens infectie met SARS-CoV-2

Het RAAS-systeem en ACE
Het renine-angiotensine-aldosteronsysteem (RAAS) reguleert de bloeddruk en de vochtbalans. De RAS genereert angiotensine II (Ang II), dat zich bindt aan receptoren in de hersenen, nieren, vasculatuur en immuunsysteem. Angiotensinogen (Agt) is een substraat van renine. Renin splitst Agt op Angiotensin I (Ang I), en wordt vervolgens door ACE gesplitst op Ang II. Renine komt voornamelijk tot uiting in de nieren. Mastcellen zijn betrokken bij de afgifte van renine. In 2006 werd gevonden dat de afgifte van renine door cardiale mastcellen kan worden veroorzaakt door ischemie (Classical Renin-Angiotensin System in Kidney Physiology, Comprehensive Physiology, Vol. 4 Issue 3, July 2014)).

Bradykinine is een substraat voor ACE. Bradykinie  heeft vaatverwijdende en natriuretische eigenschappen. ACE inactiveert bradykinine en staat daarom bekend als kininase II. ACE-remmers verhogen het niveau van bradykinine (Unraveling the pivotal role of Bradykinin in ACE inhibitor activity, American Journal of Cardiovascular Drugs, 3 June 2016). De remming van ACE wordt geassocieerd met angio-oedeem (Effect of bradykinin receptor antagonism on ACE inhibitor-associated angioedema, Journal of Allergy and Clinical Immunology, July 2017, Vol. 140 Issue 1).

ACE-AngII moet in evenwicht zijn met ACE2-Ang 1-7
ACE2 splitst een residu van Ang I om Ang 1-9 te vormen en zet Ang II om in vaatverwijdend Ang 1-7 (NCBI: gene ID), dat Ang II blokkeert en ACE remt ((ACE2, a new regulator of the renin-angiotensin system, Trends in Endocrinology and Metabolism, May 2004). In een studie uit 2008 werd voorgesteld dat verlies van ACE2-expressie en lokaal verhoogde Ang II-productie lekkage van longvaten veroorzaakte na SARS-infectie. Penninger noemt de katalytische inactivering van metabolieten van bradykinine door ACE2 als risicofactor (The discovery of angiotensin-converting enzyme 2 and its role in acute lung injury in mice, Experimental Physiology, 25 April 2008). Vermindering van ACE2 tijdens infectie met SARS is waarschijnlijk de oorzaak van onevenredige niveaus van bradykinine, wat tot lekkage kan leiden.

Ang II staat erom bekend een centrale rol te spelen bij endotheeldisfunctie. Ang II verhoogt niet alleen de bloeddruk via vasoconstrictie (vernauwing van bloedvaten), de werking op de Ang II type I-receptor (AT1) heeft een negatieve invloed op de vaatwand en versterkt oxidatieve stress, wat resulteert in endotheelbeschadiging en endotheelcelapoptose. Oxidatieve stress verhoogt de expressie van plasminogeenactivatorinhibitor type I (PAI-1), wat resulteert in de rekrutering en binding van ontstekingscellen aan het endotheel weefsel, wat leidt tot ontsteking en trombose (A review of the role of bradykinin and nitric oxide in the cardioprotective action of Angiotensin-Converting Enzyme Inhibitors: Focus on Perindopril, Cardiology and Therapy 8, 1 October 2019).

Verbetering van ACE2 kan de sleutel zijn (New agents modulating the renin-angiotensin-aldosterone system- Will there be a new therapeutic option?, Experimental Biology and Medicine, 19 July 2016). Een recente follow-up van de studie van Penninger uit 2008 stelt menselijke recombinant ACE2 voor voor een ander mechanisme dat plausibel lijkt: de studie uit 2020 toont remming van het virus door hrsACE2 (Inhibition of SARS-CoV-2 infections in engineered human tissues using clinical-grade hrsACE2, Cell Journal Pre-Proof, April 2020). Eerder werd een vergelijkbare therapie voorgesteld met recombinant humaan ACE2, rhACE2, om de Ang II-plasmaspiegels te verlagen en Ang 1-7 en 1-5 te verhogen (Recombinant human ACE2: acing out Ang II in ARDS therapy, Critical Care, 13 December 2017) .

Wordt vervolgd...
In het volgende onderdeel zal ik de prevalentie van trombotische voorvallen en longembolie geassocieerd met SARS-CoV-1 (2003) en SARS-CoV-2 bespreken. Twintig jaar SARS heeft duidelijk gemaakt dat stollingsstoornissen optreden in SARS-gevallen - zelfs patiënten die terloops worden beschouwd als "niet in gevaar" lopen in feite risico op trombotische voorvallen. Houd er rekening mee dat al deze mechanismen, van ACE2-stoornis en ontregeling van het RAAS, ontsteking, trombose en trombocytopenie (stollingsstoornissen) en cytokinestorm met elkaar verweven zijn; deze mechanismen en pathologieën dragen bij tot verslechtering in ernstige gevallen van COVID-19.

 

Pathways to deterioration in SARS-CoV-2 I: is enhancement of ACE2 in the RAAS system key?

In this "Deterioration series", I will elaborate on the mechanisms underlying the severity of SARS-CoV-2 infection. I made this summary of mechanisms known to contribute to severe complications in COVID-19 patients. There is an ever growing body of knowledge since SARS-CoV-1 (2003), the first SARS-Coronavirus that was associatied with the same mechanisms as are observed in SARS-CoV-2. From this BoK and SARS-CoV-2 reports can be gathered that the following mechanisms are involved: 

Intertwined! Mechanisms of COVID/ SARS-CoV-2 pathogenesis

In this message, I will discuss the influence of SARS-CoV-2 on dysregulation of the Renin-Angiotensin-Aldosterone System (RAS/RAAS). Notably, disruption of ACE2 upregulates Angiotensin II (Ang II). Ang II in its turn increases blood pressure. Actions on the Ang II type I receptor (AT1) adversely affects the vascular wall and enhances oxidative stress, resulting in endothelial damage and endothelial cell apoptosis. Oxidative stress increases expression of plasminogen activator inhibitor type I, resulting in the recruitment and binding of inflammatory cells to the endothelium, which leads to inflammation and thrombosis. Aside from ACE2, there is ACE. Bradykinin is a substrate for ACE. Bradykinin has vasodilator and natriuretic properties. ACE inactivates bradykinin and is therefore known as kininase II. ACE inhibition increases the level of bradykinin, rendering the vasculature permeable. Thus, reduction of ACE adversely affects degradation of bradykinin, increasing the risk of 'leaking' vessels.

How ACE2 is affected by SARS-CoV-2 pathogens

The spike glycoprotein of SARS-CoV-2 is known to use human (and other mammal, with the exception of some rodents) Angiotensin Converting Enzyme 2-receptors. The ACE2-receptor is found in type II alveolar cells (AT2) of the lungs, esophagus epithelial cells, enterocytes from ileum and colon, nasal cavity, vascular endothelia, renal tissue (kidneys), epithelia of the small intestine, testes and on the epithelial cells of oral mucosa (High expression of ACE2 receptor of 2019-nCoV on the epithelial cells of oral mucosa, International Journal of Oral Science, 24 February 2020), as well as in the brain stem and neural cortex. SARS invades ACE2-enriched cells, only to replicate itself very quickly in order to contract other cells. The infection of type II pneumocytes and release of virus in the respiratory tract with close proximity to the pulmonary capillary bed has been thought to allow systemic spread of virus to distant organs (ACE2 Receptor Expression and SARS Infection Depend on Differentiation of Human Airway Epithelia, Journal of Virology, December 2005). 

Uncertainty: is ARDS an adequate classification?
It is yet unclear what exactly constitutes sudden deterioration in critically ill SARS-CoV-2 patients. A sudden deterioration in patients with oxygen deprivation is labelled "Acute Respiratory Distress Syndrome" (ARDS). It is prone to doubt whether ARDS, characterized by bilateral infiltrates, hypoxaemia and dyspnea (Acute Lung Injury and ARDS: Pathophysiology and Treatment, Missouri Medicine, Jul-Aug 2010), is an adequate classification for the pathophysiology associated with SARS-CoV-2 (COVID-19 Pneumonia: ARDS or not?, Critical Care 24, Article number 154 (2020)). In general, the role of specific pathogens for development of ARDS is considered to be difficult to assess (Acute Respiratory Distress Syndrome and Pneumonia: A Comprehensive Review of Clinical Data, Clinical Infectious Diseases, Vol. 43 Issue 6, 15 September 2006).

Pathological findings of an early COVID case study: overactivation of T cells
In one case concerning pathological findings of COVID-19 associated with ARDS, oxygen saturation remained above 95% until the fourteenth day of illness. Day 14 of the illness, hypoxaemia worsened and oxygen saturation dropped below 60%, followed by cardiac arrest. Bilateral diffuse alveolar damage with cellular fibromyxoid exudates was observed, as well as peeling of pneumocytes and hyaline membrane formation in the right lung; the left lung displayed pulmonary oedema with hyaline formation. These findings were regarded suggestive of early-onset ARDS. Mononuclear inflammatory infiltrates dominated by lymphocytes were seen in both lungs. One of major contributions to deterioration in this case was likely an overactivation of T cells. While peripheral CD4 and CD8 T cells were reduced, they were hyperactivated. High proportions of HLA-DR (presenting antigen and providing a ligand to T cells) and CD38 (glycoprotein on the surface of immune cells) were seen. Concentrations of CCR6+ Th17 (T-helper cells) were high, CD8 T cells were found to harbor high concentrations of cytotoxic granulates (Pathological findings of COVID-19 associated with ARDS, The Lancet, February 18 2020). Similar observations were made in a 2005 study (ACE2 Receptor Expression and SARS Infection Depend on Differentiation of Human Airway Epithelia, Journal of Virology, December 2005).

Cytokine storm and invasion of the Central Nervous System
Cytokine storm, an overreaction of the hosts' immune system, is coined to explain the mechanisms behind sudden deterioration (The cytokine release syndrome of severe COVID-19 and IL-6R antagonist Tocilizumab may be the key, International Journal of Antimicrobial Agents, 29 March 2020; see also Cytokine release syndrome in severe COVID-19, AAAS, 17 April 2020). Another pathway could be the invasion of the Central Nervous System and involving of the brain stem, which could explain patients' oxygen starvation. Both pathways have recently been rejected by researchers, as supplied data is still insufficient to prove that either cytokine storm or CNS involvement plays a major role in oxygen starvation- beside multiple organ failure.

Multi-factor assessment
Foremost, it must be noted that a homogeneous kind of ARDS does not exist. ARDS is a definition to describe acute onset of hypoxaemia (ARDS subphenotypes: Understanding a heterogeneous syndrome, Critical Care, 24 March 2020). Likewise, immunity response in SARS-CoV-2 patients is heterogeneous: treatment of immunity response is not a 'one size fits all' matter. This is even further complicated by the fact that immunomodulation should not impair antiviral activity in the host.

What should and could be learned from SARS-1 (2003) when it comes to assessing medical factors?
A comprehensive, multi-factor assessment could be of use to explain SARS' pathways from invasion to deterioration. The body is a system in which the affected parts each contribute to severity of disease. Immunity and cardiovascular mechanisms are intertwined, therefore these mechanisms cannot be considered to contribute independently to deterioration. These systems are a basic necessity to keep the machine going. I'd say that SARS causes imbalance in homestasis, characterized by ACE2 impairment and imbalance of the RAS, damage to endothelial tissue, instigation of the inflammatory soup/cascade, thrombotic events- given that these mechanisms enhance each other into an overdrive mode. The interplay between inflammation and venous thromboembolism is not simply one of cause and consequence, but an intertwined interaction. For example, see: 'The role of inflammation in Venous Thromboembolism', Frontiers in Pediatrics, 23 May 2018, 2018:6:142. What SARS-CoV-1 has made clear, is that coagulation disorders occur frequently in severe cases. Endothelial damage may be an early stage cause of an inflammation cascade, followed by thrombotic events. In a 2004 SARS review, it was said that the 2003 SARS epidemic experience should warrant increased vigilance against stroke and other thrombotic SARS-related events in future outbreaks of coronaviruses (Large artery ischaemic stroke in SARS, Journal of Neurology 251, October 2004).

I'll get to what has been intriguing me in the context of other disease case studies (cardiovascular) and what caught my attention again during the early phase of the SARS-CoV-2 pandemic: that is the plausible role of ACE2 as part of the RAAS system and the detrimental loss of ACE2 during infection with SARS-CoV-2.

The RAAS system and ACE
The Renin-Angiotensin-Aldosterone System (RAAS) regulates blood pressure and fluid balance. The RAS generates angiotensin II (Ang II), which binds to receptors in the brain, kidneys, vasculature and immune system. Angiotensinogen (Agt) is a substrate of renin. Renin cleaves Agt to Angiotensin I (Ang I), subsequently to be cleaved by ACE to Ang II. Renin is primarily expressed in the kidneys. Mast cells are involved in the release of renin. It was found in 2006 that release of renin by cardiac mast cells can be induced by ischemia (Classical Renin-Angiotensin System in Kidney Physiology, Comprehensive Physiology, Vol. 4 Issue 3, July 2014).

Bradykinin is a substrate for ACE. Bradykinin has vasodilator and natriuretic properties. ACE inactivates bradykinin and is therefore known as kininase II. ACE inhibitors increase the level of bradykinin (Unraveling the pivotal role of Bradykinin in ACE inhibitor activity, American Journal of Cardiovascular Drugs, 3 June 2016). The inhibition of ACE is associated with angioedema (Effect of bradykinin receptor antagonism on ACE inhibitor-associated angioedema, Journal of Allergy and Clinical Immunology, July 2017, Vol. 140 Issue 1).

ACE-AngII should be in balance with ACE2-Ang 1-7
ACE2 cleaves a residue from Ang I to form Ang 1-9 and converts Ang II to vasodilator Ang 1-7 (NCBI: gene ID), which blocks Ang II and inhibits ACE (ACE2, a new regulator of the renin-angiotensin system, Trends in Endocrinology and Metabolism, May 2004). In a 2008 study, it was proposed that loss of ACE2 expression and locally increased Ang II production triggered leakage of pulmonary blood vessels after SARS infection. Penninger mentions the catalytic inactivation of bradykinin metabolites by ACE2 (The discovery of angiotensin-converting enzyme 2 and its role in acute lung injury in mice, Experimental Physiology, 25 April 2008). Impairment of ACE2 during infection with SARS is likely the cause of disproportionate levels of bradykinin, which could lead to leakage.

Ang II is known to play a central role in endothelial dysfunction. Not only does Ang II increase blood pressure via vasoconstriction (the narrowing of blood vessels), actions on the Ang II type I receptor (AT1) adversely affects the vascular wall and enhances oxidative stress, resulting in endothelial damage and endothelial cell apoptosis. Oxidative stress increases expression of plasminogen activator inhibitor type I, resulting in the recruitment and binding of inflammatory cells to the endothelium, which leads to inflammation and thrombosis (A review of the role of bradykinin and nitric oxide in the cardioprotective action of Angiotensin-Converting Enzyme Inhibitors: Focus on Perindopril, Cardiology and Therapy 8, 1 October 2019).

Enhancement of ACE2 could be key (New agents modulating the renin-angiotensin-aldosterone system- Will there be a new therapeutic option?, Experimental Biology and Medicine, 19 July 2016). A recent follow-up of the 2008 study by Penninger proposes human recombinant ACE2 for another mechanism that seems plausible: the 2020 study shows inhibition of the virus by hrsACE2 (Inhibition of SARS-CoV-2 infections in engineered human tissues using clinical-grade hrsACE2, Cell Journal Pre-Proof, April 2020). Previously, a similar therapy was proposed involving recombinant human ACE2, rhACE2, to decrease plasma Ang II levels and increase Ang 1-7 and 1-5 (Recombinant human ACE2: acing out Ang II in ARDS therapy, Critical Care, 13 December 2017).

Next feature
In next feature, I will discuss the prevalence of thrombotic events and pulmonary embolism associated with SARS-CoV-1 (2003) and SARS-CoV-2. Twenty years of SARS has made clear that coagulation disorders occur in SARS cases- even patients who are casually deemed "not to be at risk" are in fact at risk of thrombotic events. Keep in mind that all of these mechanisms, from ACE2 impairment and dysregulation of the RAS, inflammation, thrombosis and thrombocytopenia (coagulation disorders) and cytokine storm are intertwined; these mechanisms and pathologies contribute to deterioration in severe cases of COVID-19.

The RAS and its relation to inflammation and coagulation disorders in COVID-19

 

In summary: slides